NATL INST OF STAND & TECH

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NBS

PUBLICATIONS

NBS SPECIAL PUBLICATION 260-82

U.S. DEPARTMENT OF COMMERCE/National Bureau of Standards

Standard Reference Materials:

White Opal Glass

Diffuse Spectral

Reflectance Standards

for the Visible Spectrum

(SRM's 2015 and 2016)

-€C

100

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260-d2

1983

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NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of

physical and chemical and materials measurement; coordinates the system with measurement

systems of other nations and furnishes essential services leading to accurate and uniform

physical and chemical measurement throughout the Nation's scientific community, industry,

and commerce; conducts materials research leading to improved methods of measurement,

standards, and data on the properties of materials needed by industry, commerce, educational

institutions, and Government; provides advisory and research services to other Government

agencies; develops, produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers:

Absolute Physical Quantities 2 — Radiation Research — Chemical Physics —

Analytical Chemistry — Materials Science

THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement capabilities;

provides engineering measurement traceability services; develops test methods and proposes

engineering standards and code changes; develops and proposes new engineering practices;

and develops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers:

Applied Mathematics — Electronics and Electrical Engineering2 — Manufacturing

Engineering — Building Technology — Fire Research — Chemical Engineering2

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of computer technology to improve effectiveness and

economy in Government operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards

guidelines, and managing Federal participation in ADP voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and

provides the technical foundation for computer-related policies of the Federal Government.

The Institute consists of the following centers:

Programming Science and Technology — Computer Systems Engineering.

'Headquarters and Laboratories at Gaithersburg, M D, unless otherwise noted; mailing address Washington, DC 20234. 'Some divisions within the center are located at Boulder, CO 80303.
pi' dTA:.V Ai(W

Standard Reference Materials: JJ(JN 1

4

White Opal Glass Diffuse Spectral

Reflectance Standards for the Visible

Spectrum (SRM's 2015 and 2016)

Victor R. Weidner

Radiometric Physics Division

Center for Radiation Research

National Bureau of Standards

Washington, DC 20234

*<"»EAU O*

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued April 1983
Library of Congress Catalog Card Number: 83-600516

National Bureau of Standards Special Publication 260-82

Natl. Bur. Stand. (U.S.), Spec. Publ. 260-82, 33 pages (Apr. 1983)

CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1983

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

Price $3.75

(Add 25 percent for other than U.S. mailing)
PREFACE

Standard Reference Materials (SRM's) as defined by the

National Bureau of Standards are well-characterized materials

produced in quantity and certified for one or more physical

or chemical properties. They are used to assure the accuracy

and compatibility of measurements throughout the Nation.

SRM's are widely used as primary standards in many diverse

fields in science, industry, and technology, both within the

United States and throughout the world. They are also used

extensively in the fields of environmental and clinical analysis. In many applications, traceability of quality control

and measurement processes to the national measurement system

are carried out through the mechanism and use of SRM's. For

many of the Nation's scientists and technologists it is

therefore of more than passing interest to know the details

of the measurements made at MBS in arriving at the certified

values of the SRM's produced. An MBS series of papers, of

which this publication is a member, called the NBS Special

Publication - 260 Series , is reserved for this purpose.

This 260 Series is dedicated to the dissemination of

information on different phases of the preparation, measurement, certification and use of NBS-SRM's. In general, much

more detail will be found in these papers than is generally

allowed, or desirable, in scientific journal articles. This

enables the user to assess the validity and accuracy of the

measurement processes employed, to judge the statistical

analysis, and to learn details of techniques and methods

utilized for work entailing the greatest care and accuracy.

These papers also should provide sufficient additional information not found on the certificate so that new applications

in diverse fields not foreseen at the time the SRM was originally issued will be sought and found.

Inquiries concerning the technical content of this paper

should be directed to the author. Other questions concerned

with the availability, delivery, price, and so forth will

receive prompt attention from:

Office of Standard Reference Materials

National Bureau of Standards

Washington, D.C. 20234

George A. Ur iano, Chief

Office of Standard Reference Materials

1 1

1
OTHER NBS PUBLICATIONS IN THIS SERIES

Catalog of NBS Standard Reference Materials

(1981-83 edition), R. W. Seward, ed., NBS

Spec. Publ. 260 (November 1981).

Michaelis, R. E., and Wyman, L. L. Standard

Reference Materials: Preparation of White Cast

Iron Spectrochemical Standards. NBS Misc.

Publ. 260-1 (June 1964). CO M 74- 1 1 06 I * * Michaelis, R. E., Wyman, L. L., and Flitsch, R., Standard Reference Materials: Preparation of

NBS Copper-Base Spectrochemical Standards.

NBS Misc. Publ. 260-2 (October 1964). COM74-

1 1063**

Michaelis, R. E., Yakowitz, H., and Moore, G. A., Standard Reference Materials: Metallographic

Characterization of an NBS Spectrometric LowAlloy Steel Standard. NBS Misc. Publ. 260-3

(October 1964). COM74-1 1060**

Hague, J. L. Mears, T. W., and Michaelis, R. E., Standard Reference Materials: Sources of

Information, NBS Misc. Publ. 260-4 (February

1965). COM74-U059

Alvarez, R., and Flitsch R., Standard Reference

Materials: Accuracy of Solution X-Ray Spectrometric Analysis of Copper-Base Alloys. NBS

Misc. Publ. 260-5 (March 1965). PB 168068**

Shultz, J. L, Standard Reference Materials:

Methods for the Chemical Analysis of White

Cast Iron Standards, NBS Misc. Publ. 260-6

(July 1975). COM74-1 1068**

Bell, R. K., Standard Reference Materials:

Methods for the Chemical Analysis of NBS

Copper-Base Spectrochemical Standards. NBS

Misc. Publ. 260-7 (October 1965). COM74-

1 1067**

Richmond, M.S., Standard Reference Materials:

Analysis of Uranium Concentrates at the

National Bureau of Standards. NBS Misc. Publ. 260-8 (December 1965). COM 74- 1 1066**

Anspach, S. C, Cavallo, L. M. Garfinkel, S. B. Hutchinson, J. M. R., and Smith, C. N., Standard Reference Materials: Half Lives of Materials

Used in the Preparation of Standard Reference

Materials of Nineteen Radioactive Nuclides

Issued by the National Bureau of Standards

NBS Misc. Publ. 260-9 (November 1965).

COM 74- 1 1065**

Yakowitz, H., Vieth, D. L., Heinrich, K. F. J., and

Michaelis, R. E., Standard Reference Materials:

Homogeneity Characterization on NBS Spectrometric Standards II: Cartridge Brass and LowAlloy Steel, NBS Misc. Publ. 260-10 (December

1965). COM74-I 1064**

Napolitano, A., and Hawkins, E. G., Standard

Reference Materials: Viscosity of Standard

Lead-Silica Glass, NBS Misc. Publ. 260-11

(November 1966). NBS Misc. Publ. 260-11**

Yakowitz, H., Vieth, D. L., and Michaelis, R. E., Standard Reference Materials: Homogeneity

Characterization of NBS Spectrometric Standards III: White Cast Iron and Stainless Steel Powder Compact, NBS Misc. Publ. 260-12

(September 1966). NBS Misc. Publ. 260-12**

Spijkerman, J. L., Snediker, D. K., Ruegg, F. C,

and DeVoe, J. R., Standard Reference Materials: Mossbauer Spectroscopy Standard for the Chemical Shift of Iron Compounds, NBS Misc.

Publ. 260-13 (July 1967). NBS Misc. Publ.

260-13**

Menis, O., and Sterling, J. T., Standard Reference

Materials: Determination of Oxygen in Ferrous

Materials - SRM 1090, 1091, and 1092, NBS

Misc. Publ. 260-14 (September 1966). NBS Misc.

Publ. 260-14**

Passaglia, E., and Shouse, P. J. Standard Refer- ence Materials: Recommended Method of Use

of Standard Light-Sensitive Paper for Calibrating Carbon Arcs Used in Testing Textiles for Colorfastness to Light, NBS Misc. Publ. 260-15

(June 1967). (Replaced by NBS Spec. Publ.

260-41.)

Yakowitz, H., Michaelis, R. E., and Vieth, D. L., Standard Reference Materials: Homogeneity

Characterization of NBS Spectrometric Standards IV: Preparation and Microprobe Characterization of W-20% MO Alloy Fabricated by

Powder Metallurgical Methods, NBS Spec.

Publ. 260-16 (January 1969). COM74-1 1062**

Catanzaro, E. J., Champion, C. E., Garner, E. L., Marinenko, G., Sappenfield, K. M., and Shields,

W. R. Standard Reference Materials: Boric

Acid; lsotopic and Assay Standard Reference

Materials, NBS Spec. Publ. 260-17 (February

1970). Out ol Print
Geller, S. B., Mantek, P. A., and Cleveland, N. G., Standard Reference Materials: Calibration of NBS Secondary Standard Magnetic Tape

(Computer Amplitude Reference) Using the

Reference Tape Amplitude Measurement

"Process A, "NBS Spec. Publ. 260-18 (November

1969). (See NBS Spec. Publ. 260-29.)

Paule, R. C, and Mandel, J., Standard Reference

Materials: Analysis of Interlaboratory Measurements on the Vapor Pressure of Gold (Certifica- tion of Standard Reference Material 745). NBS

Spec. Publ. 260-19 (January 1970). PB19007I**

Paule, R. C, and Mandel, J., Standard Reference

Materials: Analysis of Interlaboratory Measurements on the Vapor Pressures of Cadmium and

Silver, NBS Spec. Publ. 260-21 (January 1971).

COM74-1 1359**

Yakowitz, H., Fiori, C. E., and Michaelis, R. E., Standard Reference Materials: Homogeneity

Characterization of Fe-3 Si Alloy, NBS Spec.

Publ. 260-22 (February 1971). COM74-1 1357**

Napolitano, A., and Hawkins, E. G., Standard

Reference Materials: Viscosity of a Standard

Borosilicate Glass, NBS Spec. Publ. 260-23

(December 1970). COM7 1-00 1 57**

Sappenfield, K. M., Marineko, G., and Hague, J. L., Standard Reference Materials: Comparison

of Redox Standards, NBS Spec. Publ. 260-24

(January 1972). COM72-50058**

Hicho, G. E., Yakowitz, H., Rasberry, S. D., and

Michaelis, R. E., Standard Reference Materials:

A Standard Reference Material Containing

Nominally Four Percent Austenite, NBS Spec.

Publ. 260-25 (February 1971). COM74-I 1356**

Martin, J. F., Standard Reference Materials:

National Bureau of Standards-US Steel Corportion Joint Program for Determining Oxygen and

Nitrogen in Steel, NBS Spec. Publ. 260-26

(February 1971). 85 cents* PB 81 176620

Garner, E. L., Machlan, L. A., and Shields, W. R., Standard Reference Materials: Uranium

lsotopic Standard Reference Materials, NBS

Spec. Publ. 260-27 (April 1971). COM74-

I 1358**

Heinrich, K. F. J., Myklebust, R. L., Rasberry, S. D., and Michaelis, R. E., Standard Reference

Materials: Preparation and Evaluation of

SRM's 481 and 482 Gold-Silver and GoldCopper Alloys for Microanalysis, NBS Spec.

Publ. 260-28 (August 1971). COM7 1-50365**

Geller, S. B., Standard Reference Materials: Cali- bration of NBS Secondary Standard MagneticTape (Computer Amplitude Reference) Using

the Reference Tape Amplitude Measurement

"Process A-Model 2," NBS Spec. Publ. 260-29

(June 1971). COM7I-50282

Gorozhanina, R. S., Freedman, A. Y., and

Shaievitch, A. B. (translated by M. C. Selby),

Standard Reference Materials: Standard

Samples Issued in the USSR (A Translation

from the Russian). NBS Spec. Publ. 260-30 (June

1971). COM7I-50283**

Hust, J. G., and Sparks, L. L., Standard Reference

Materials: Thermal Conductivity of Electrolytic Iron SRM 734 from 4 to 300 K, NBS Spec. Publ. 260-31 (November 1971). COM7 1-50563**

Mavrodineanu, R., and Lazar, J. W., Standard

Reference Materials: Standard Quartz Cuvettes,

for High Accuracy Spectrophotometry, NBS

Spec. Publ. 260-32 (December 1973). 55 cents* SN003-003-0I213-I

Wagner, H. L., Standard Reference Materials:

Comparison of Original and Supplemental

SRM 705, Narrow Molecular Weight Distri- bution Polystyrene, NBS Spec. Publ. 260-33

(May 1972). COM72-50526**

Sparks, L. L., and Hust, J. G., Standard Reference

Materials: Thermoelectric Voltage, NBS Spec.

Publ. 260-34, (April 1972). COM72-5037 1 ** Sparks, L. L., and Hust, J. G., Standard Refer- ence Materials: Thermal Conductivity of

Austenitic Stainless Steel, SRM 735 from 5 to 280 K, NBS Spec. Publ. 260-35 (April 1972.) 35 cents* COM72-50368**

Cali, J. P., Mandel, J., Moore, L. J., and Young, D.

S., Standard Reference Materials: A Referee

Method for the Determination of Calcium in Serum, NBS SRM 915, NBS Spec. Publ. 260-36

(May 1972). COM72-50527**

Shultz, J. I. Bell., R. K. Rains, T. C, and Menis,

O., Standard Reference Materials: Methods of Analysis of NBS Clay Standards, NBS Spec.

Publ. 260-37 (June 1972). COM72-50692**

Richmond, J. C, and Hsia, J. J., Standard Refer- ence Materials: Preparation and Calibration of

Standards of Spectral Specular Reflectance,

NBS Spec. Publ. 260-38 (May 1972). COM72-

50528**

Clark, A. F., Denson, V.A., Hust, J. G., and

Powell, R. L., Standard Reference Materials

The Eddy Current Decay Method for Resistivity

Characterization of High-Purity Metals, NBS

Spec. Publ. 260-39 (May 1972). COM72-50529**

V
McAdie, H. G., Garn, P.D., and Menis, O., Standard Reference Materials: Selection of Thermal

Analysis Temperature Standards Through a Cooperative Study (SRM 758, 759, 760), NBS

Spec. Publ. 260-40 (August 1972.) COM72-

50776**

Wood, L. A., and Shouse, P. J., Standard

Reference Materials: Use of Standard LightSensitive Paper for Calibrating Carbon Arcs Used in Testing Textiles for Colorfastness to Light, NBS Spec. Publ. 260-41 (August 1972)

COM72-50775**

Wagner, H. L. and Verdier, P. H., eds.. Standard

Reference Materials: The Characterization of Linear Polyethylene, SRM 1475, NBS Spec.

Publ. 260-42 (September 1972). COM72-

50944**

Yakowitz, H., Ruff, A. W., and Michaelis, R. E., Standard Reference Materials: Preparation, and

Homogeneity Characterization of an Austenitic

lron-Chromium-Nickel Alloy, NBS Spec. Publ.

260-43 (November 1972). COM 73-50760**

Schooley, J. F., Soulen, R. J., Jr., and Evans, G. A.,

Jr., Standard Reference Materials: Preparation

and Use of Superconductive Fixed Point

Devices, SRM 767, NBS Spec. Publ. 260-44

(December 1972). COM73-50037**

Greifer, B., Maienthal, E. J. Rains, T. C, and

Rasberry, S. D., Standard Reference Materials:

Powdered Lead-Based Paint, SRM 1579, NBS

Spec. Publ. 260-45 (March 1973). COM73-

50226**

Hust, J. G., and Giarratano, P. J., Standard Refer- ence Materials: Thermal Conductivity and

Electrical Resistivity Standard Reference Materials: Austenitic Stainless Steel, SRM's 735 and

798, from 4 to 1200 k, NBS Spec. Publ. 260-46

(March 1975). SN003-003-0 1 278-5

Hust, J. G., Standard Reference Materials: Electrical Resistivity of Electrolytic Iron, SRM 797,

and Austenitic Stainless Steel, SRM 798, from 5 to 280 K, NBS Spec. Publ. 260-47 (February

1974). COM74-50I76**

Mangum, B. W., and Wise, J. A., Standard Refer- ence Materials: Description and Use of Precision

Thermometers for the Clinical Laboratory,

SRM 933 and SRM 934, NBS Spec. Publ. 260-48

(May 1974). 60 cents* SN003-003-0 1 278-5

Carpenter, B. S., and Reimer, G. M., Standard

Reference Materials Calibrated Glass Standards for Fission Track Use, NBS Spec. Publ. 260-49 (November 1974). COM74-5U85

Hust, J. G., and Giarratano, P. J., Standard Refer- ence Materials: Thermal Conductivity and Electrical Resistivity Standard Reference Materials:

Electrolytic Iron, SRM's 734 and 797 from 4 to 1000 K, NBS Spec. Publ. 260-50 (June 1975).

$1.00* SN003-003-0 1425-7 Mavrodineanu, R., and Baldwin, J. R., Standard

Reference Materials: Glass Filters As a Standard

Reference Material for Spectrophotometry;

Selection; Preparation; Certification; Use-SRM

930, NBS Spec. Publ. 260-51 (November 1975).

$1.90* SN003-003-01481-8

Hust, J. G., and Giarratano, P. J., Standard Refer- ence Materials: Thermal Conductivity and Electrical Resistivity Standard Reference Materials

730 and 799, from 4 to 3000 K, NBS Spec. Publ.

260-52 (September 1975). $1.05* SN003-003-

01464-8

Durst, R. A., Standard Reference Materials:

Standardization of pH Measurements, NBS

Spec. Publ. 260-53 (December 1975, Revised).

$1.05 SN003-003-01551-2

Burke, R. W., and Mavrodineanu, R. Standard

Reference Materials: Certification and Use of

Acidic Potassium Dichromate Solutions as an

Ultraviolet Absorbance Standard, NBS Spec.

Publ. 260-54 (August 1977). $3.00* SN003-003-

01828-7

Ditmars, D. A., Cezairliyan, A., lshihara, S., and

Douglas, T. B., Standard Reference Materials:

Enthalpy and Heat Capacity; Molybdenum

SRM 781, from 273 to 2800 K, NBS Spec. Publ. 260-55 (September 1977). $2.20* SN003-003-

01836-8

Powell, R. L., Sparks, L. L., and Hust, J. G.,

Standard Reference Materials: Standard

Thermocouple Materials, Pt.67: SRM 1967, NBS

Spec. Publ. 260-56 (February 1978). $2.20*

SN003-003-0 18864

Cali, J. P. and Plebanski, T., Guide to United

States Reference Materials, NBS Spec. Publ. 260-57 (February 1978). $2.20* PB 277173

Barnes, J. D., and Martin, G. M., Standard Refer- ence Materials: Polyester Film for Oxygen Gas

Transmission Measurements SRM 1470, NBS

Spec. Publ. 260-58 (June 1979) $2.00* SN003-

003-02077

Chang, T., and Kahn, A. H. Standard Reference

Materials: Electron Paramagnetic Resonance

Intensity Standard; SRM 2601, NBS Spec.

Publ. 260-59 (August 1978) $2.30* SN003-

003-01975-5

vi
Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel, J., and Moody, J. R., Standard Refer- ence Materials: A Reference Method for the Determination of Sodium in Serum, NBS Spec.

Publ. 260-60 (August 1978). $3.00* SN003-003

01978-0

Verdier, P. H., and Wagner. H. L., Standard Refer- ence Materials: The Characterization of Linear

Polyethylene (SRM 1482, 1483, 1484), NBS

Spec. Publ. 260-61 (December 1978). $1.70*

SN003-003-02006-1

Soulen, R. J., and Dove, R. B., Standard Reference

Materials: Temperature Reference Standard

for Use Below 0.5 K (SRM 768). NBS Spec.

Publ. 260-62 (April 1979). $2.30* SN003-003-

02047-8

Velapoldi, R. A., Paule, R. C, Schaffer, R. Mandel, J., Machlan, L. A., and Gramlich, J. W.,

Standard Reference Materials: A Reference

Method for the Determination of Potassium in Serum. NBS Spec. Publ. 260-63 (May 1979).

$3.75* SN003-003-02068

Velapoldi, R. A., and Mielenz, K. D., Standard

Reference Materials: A Fluorescence Standard

Reference Material Quinine Sulfate Dihydrate

(SRM 936), NBS Spec. Publ. 260-64 (January

1980). $4.25* SN003-003-02 148-2 Marinenko, R. B., Heinrich, K. F. J., and Ruegg,

F. C, Standard Reference Materials: MicroHomogeneity Studies of NBS Standard Reference

Materials, NBS Research Materials, and Other

Related Samples. NBS Spec. Publ. 260-65

(September 1979). $3.50* SN003-003-02 1 14-

Venable, W. H., Jr., and Eckerle, K... L., Standard

Reference Materials: Didymium Glass Filters for Calibrating the Wavelength Scale of Spectrophotometers (SRM 2009, 2010, 2013). NBS Spec.

Publ. 260-66 (October 1979). $3.50* SN003-003-

02127-0

Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel,

J., Murphy, T. J., and Gramlich, J. W., Standard

Reference Materials: A Reference Method for the Determination of Chloride in Serum, NBS Spec.

Publ. 260-67 (November 1979). $3.75* SN003-

003-02 1 36-9 Mavrodineanu, R. and Baldwin, J. R., Standard

Reference Materials: Metal-On-Quartz Filters as a Standard Reference Material for Spectrophotometry-SRM 2031, NBS Spec. Publ. 260-88

(April 1980). $4.25* SN003-003-02 1 67-9

Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel, J., Machlan, L. A., Garner, E. L., and

Rains, T. C, Standard Reference Materials: A

Reference Method lor the Determination of

Lithium in Serum, NBS Spec. Publ. 260-69 (July)

1980). $4.25* SN003-003-02214-4

Marinenko, R. B., Biancaniello, F., Boyer, P. A., Ruff, A. W., DeRobertis, L., Standard Reference

Materials: Preparation and Characterization of an Iron-Chromium-Nickel Alloy for Microanalysis, NBS Spec. Publ. 260-70 (May 1981).

$2.50* SN003-003-02328-I

Seward, R. W., and Mavrodineanu, R., Standard

Reference Materials: Summary of the Clinical Laboratory Standards Issued by the National

Bureau of Standards, NBS Spec. Publ. 260-71

(November 1981). $6.50* SN003-003-0238 1-7 Reeder, D.J., Coxon, B., Enagonio, D., Christensen,

R. G., Schaffer, R., Howell, B. F., Paule, R. C,

Mandel, J., Standard Reference Materials: SRM

900, Antiepilepsy Drug Level Assay Standard,

NBS Spec. Publ. 260-72 (June 1981). $4.25*

SN003-003-02329-9

Interrante, C. G., and Hicho, G. E., Standard Refer- ence Materials: A Standard Reference Material

Containing Nominally Fifteen Percent Austenite

(SRM 486), NBS Spec. Publ. 260-73 (January

1982). $2.75* SN003-003-02386-8

Marinenko, R. B., Standard Reference Materials:

Preparation and Characterization of K.-411 and

K.-414 Mineral Glasses for Microanalysis: SRM

470. NBS Spec. Publ. 260-74 (April 1982).

$3.50 SN003-003-023-95-7

Weidner, V. R., Hsia, J. J., Standard Reference

Materials: Preparation and Calibration of First Surface Aluminum Mirror Specular Reflectance

Standards (SRM 2003a), NBS Spec. Publ. 260-75

(May 1982). $3.75 SN003-003-023-99-0

Hicho, G. E. and Eaton, E. E., Standard Reference

Materials: A Standard Reference Material

Containing Nominally Five Percent Austenite

(SRM 485a), NBS Spec. Publ. 260-76 (August

1982). $3.50 SN003-003-024-33-3

Furukawa, G. T., Riddle, J. L., Bigge, W. G., and

Pfieffer, E. R., Standard Reference Materials:

Application of Some Metal SRM's as Thermometry Fixed Points, NBS Spec. Publ. 260-77

(August 1982). $6.00 SN003-003-024-34-

vi i
Hicho, G. E. and Eaton, E. E., Standard Reference

Materials: Standard Reference Material Containing Nominally Thirty Percent Austenite (SRM

487), NBS Spec. Publ. 260-78 (September 1982).

S3.75 SN003-003-024-35-0

Richmond, J. C, Hsia, J. J., Weidner, V. R., and

Wilmering, D. B., Standard Reference Materials:

Second Surface Mirror Standards of Specular

Spectral Reflectance (SRM's 2023, 2024, 2025),

NBS Spec. Publ. 260-79 (October 1982). $4.50

SN003-003-024-47-3

Schaffer, R., Mandel, J., Sun, T., Cohen, A., and

Hertz, H. S., Standard Reference Materials:

Evaluation by an ID/ MS Method of the AACC

Reference Method for Serum Glucose, NBS

Spec. Publ. 260-80 (October 1982). $4.75 SN003-

003-024-43-1

Burke, R. W., Mavrodineanu, R. (NBS retired).

Standard Reference Materials: Accuracy in Analytical Spectrophotometry, NBS Spec. Publ. 260-81 (In Press).

Weidner, V. R., Standard Reference Materials:

White Opal Glass Diffuse Spectral Reflectance

Standards for the Visible Spectrum (SRM's 2015

and 2016), NBS Spec. Publ. 260-82 (In Press).

* Send order with remittance to Superintendent

of Documents, US Government Printing Office

Washington, DC 20402. Remittance from

foreign countries should include an additional

one-fourth of the purchase price for postage.

** May be ordered from: National Technical

Information Services (NT1S). Springfield

Virginia 22151.
TABLE OF CONTENTS

Page

Preface i i i

Abstract 1

Disclaimer 1

1 . Introduction 2

2. Calibration of the SRM Vitrolites 3

3. Using the Vitrolite Reflectance Standard 4

4. Vitrolite Trans! ucency 8

5. Cleaning and Storing Vitrolite Reflectance Standards 16

6. References 17

7. Appendices 18

ix
LIST OF FIGURES

FIGURE NO. PAGE

1 . Six geometries illustrating the various possible

combinations of targets and ports commonly used in an integrating sphere of the Hardy spectrophotometer

to measure the reflectance of a sample with the

specular component either included or excluded . . . 6

2. The diffuse transmittance (plotted on an optical

density scale) to illustrate the linearity of diffuse

transmittance as a function of the Vitrolite thickness.

The data were obtained by means of the NBS hazemeter.

This instrument has a visual response detector system

with a peak response near 550 nanometers 9

3. The reflectance of Vitrolite as a function of thickness for Vitrolite backed by a white backing of

approximately 99 percent reflectance and for Vitrolite

backed by a black backing of less than one percent

reflectance. The data were obtained by means of the

NBS hazemeter. This instrument has a visual response

detector system with a peak response near 550 nanometers 11

4. The reflectance of Vitrolite can be influenced by the

backing, Vitrolite thickness, size of the Vitrolite,

and size of the integrating sphere port on which the

Vitrolite is mounted. The data in figure 4 should be

compared with the data illustrated in figures 5 and 6

where the port size and Vitrolite size are changed.

The data were obtained by means of the NBS hazemeter.

This instrument has a visual response detector system

with a peak response near 550 nanometers 12

5. The reflectance of Vitrolite can be influenced by the

backing, Vitrolite thickness, size of the Vitrolite,

and size of the integrating sphere port on which the

Vitrolite is mounted. The data in figure 5 should be

compared with the data illustrated in figures 4 and 6

where the port size and Vitrolite size are changed.

The data were obtained by means of the NBS hazemeter.

This instrument has a visual response detector system

with a peak response near 550 nanometers 13

6. The reflectance of Vitrolite can be influenced by the

backing, Vitrolite thickness, size of the Vitrolite,

and size of the integrating sphere port on which the

Vitrolite is mounted. The data in figure 6 should be

compared with the data illustrated in figures 4 and 5 where the port size and Vitrolite size are changed.

The data were obtained by means of the 'NBS hazemeter.

This instrument has a visual response detector system

with a peak response near 550 nanometers 14

x
LIST OF FIGURES, continued

FIGURE NO. PAGE

7. The percentage of incident light beam that is lost

out the edge of the Vitro! ite near the edge of the

integrating sphere post. The data were obtained for

a Vitrolite of 10 mm thickness. The light lost from

the measurement is due to the Vitrolite transl ucency

The amount of light lost depends on the dimensions

of the Vitrolite and the ratio of the sample beam

diameter to the port diameter. The data were obtained

by means of the NBS hazemeter. This instrument has

a visual response detector system with a peak response

near 550 nanometers 15

xi

Abstract

Vitrolite white opal glass has been calibrated for use as diffuse spectral reflectance standards since 1944.

Its uniformity and long-term durability make it useful as

an everyday working standard for spectrophotometry

measurements in the visible spectral range. However, its

translucency can introduce some errors in such measurements if improperly used. Prior to 1965 the Vitrolite

reflectance standards were issued with diffuse reflectance

values relative to freshly smoked magnesium oxide. Since

that date the calibration of these standards is reported

on an absolute reflectance scale or one which is relative

to a perfect diffuser. Since the completion of the NBS

reference spectrophotometer for diffuse reflectance

measurements in 1975, work on the perfection of techniques

for determining a more accurate absolute reflectance scale

has made it possible to further improve these measurements.

As a result of this effort, the Vitrolite reflectance

standards are now more accurately characterized and are being issued as a Standard Reference Material.

Key Words: diffuse; reflectance; spectrophotometry;

standard; translucency; Vitrolite.

Di scl aimer:

Certain commercial equipment, instruments, or materials

are identified in this report in order to adequately

specify the experimental procedure. Such identification

does not imply recommendation or endorsement by the

National Bureau of Standards, nor does it imply that the

materials or equipment identified are necessarily the

best available for the purpose.

1
I

1. Introduction

Vitrolite [I] 1 is a white opal glass originally manufactured in large quantities for wall tile and used for various architectural applications. The glass was produced prior to World War II. NBS retains a limited supply in the form of large

sheets of approximately 30 inches square from which the reflectance standards are selected. A large percentage of the glass is rejected because of surface defects

such as scratches and pits.

Vitrolite possesses several properties that make it useful as a reflectance

standard for the visible spectrum. These properties include; a relatively high

reflectance, good diffusion of the incident light, a fire polished surface which

can be cleaned repeatedly, and long-term stability. The glass from a given melt

is usually uniform in reflectance at any given wavelength to within ±0.2 percent.

Vitrolite is translucent enough to cause some problems in using it as a reflectance standard. However, this does not eliminate its usefulness, if proper

care is taken to avoid the geometrical conditions of illumination in which translucency errors occur. These conditions are specifically outlined for the user in

the discussion of Vitrolite transl ucency , appearing later in this paper.

Vitrolite has been calibrated and issued as working standards of spectral

reflectance by the National Bureau of Standards since 1944. The first melt from

which reflectance standards were selected was referred to as the "VI" melt. The

majority of standards issued came from melt V3 and melt V6. The original master

standard was selected in 1938 and labeled as Standard V1-G3. A back-up master was also selected at that time and referred to as Standard V1-G4. These two standards

are nearly identical in spectral reflectance and are still in use after forty

years. Standard V1-G3 has been used as a diffuse reflectance calibration standard

in the making of thousands of reflectance measurements during this period while

Standard V1-G4 has been stored. After many years of cleaning and handling,

Standard V1-G3 shows some very fine scratches; however, its reflectance relative

to V1-G4 has remained the same. The long-term stability of Vitrolite is believed

to be very good.

Most of the Vitrolite reflectance standards issued by NBS were calibrated on

a Hardy (General Electric) spectrophotometer for 6 degree incidence and hemispherical collection of reflected light, for a 10 nanometer bandpass. Some standards were calibrated on a Beckman spectrophotometer for 0/45 degree reflectance which

used a ring-collector type reflectance attachment.

The standards issued before 1965 were calibrated relative to freshly prepared

smoked magnesium oxide. After 1965 they were issued with the calibration data

relative to a perfect diffuser ("absolute" reflectance scale). The absolute

reflectance scale established in 1965 [2] was given further refinement in 1977

with the completion of the reference spectrophotometer for diffuse reflectance

[3]. The master Vitrolite calibration scale is presently maintained through

periodic recal i bration by absolute reflectance techniques, using the double-sphere

or Van den Akker method [4]. The master Vitrolite working standard is Standard

V6-D1 . This standard is calibrated on the NBS reference spectrophotometer for

diffuse reflectance by the absolute reflectance methods. The uncertainty in its

calibration is believed to be no more than ±0.0015.

figures in brackets indicate the literature references at the end of this paper.

2
2. Calibration of the SRM Vitro! ites

The SRM (Standard Reference Material) Vitrolite reflectance standards have

been calibrated on a Hardy spectrophotometer using the Vitrolite master to transfer the NBS absolute reflectance scale to these working standards. The uncertainty

in the calibration of these working standards is larger than the uncertainty

assigned to the master Vitrolite due to additional errors associated with the

performance of the transfer spectrophotometer and its data recording system.

Because of these factors, the uncertainty assigned to the working standards is

±0.010 (one percent).

Master V6-D1 is too valuable to be used on an every-day basis; therefore the

absolute scale was transferred to Standard V1-G3 which is used for day-to-day

calibration work. The transfer of the absolute reflectance scale from Master

V6-D1 to VI -G3 was accomplished by measuring V6-D1 on the transfer instrument

(Hardy spectrophotometer). The ratio of the absolute value of V6-D1 to its

measured value is then applied to the measured value of Standard V1-G3. By this

technique the absolute reflectance of Standard VI -G3 is established on a scale

directly traceable to the NBS Reference Diffuse Reflectance Instrument through the use of Master V6-D1 as a transfer standard.

The photometric scale of the Hardy spectrophotometer has some nonlinearity

and all measurements are adjusted to correct for this error. Corrections are also

made for slight errors in the wavelength scale.

The calibration of Standard V1-G3 with the specular component excluded from

the measurement could not be made by direct comparison to Master Vitrolite V6-D1

because the V6-D1 standard is only calibrated for the condition of illumination

and viewing in which the specular component is included in the measurement. The

calibration of Standard V1-G3 for the excluded specular measurement was accomplished

by first measuring the standard with the specular component included and then

inserting black cavities into the sphere to exclude the specular component. In this way the calibration of Standard V1-G3 for the excluded specular mode was accomplished by measuring its value relative to the included specular mode. The

specular component is approximately four percent of the total reflectance.

The recal i bration of Standard V1-G3 by transferring the absolute reflectance

scale from Master V6-D1 resulted in a new set of reflectance values for Standard

V1-G3. The new calibration values for Standard V1-G3 agreed with the previous

(1974) absolute reflectance calibration to within ±0.005 (one-half percent) for

both the included and excluded specular component measurements.

The calibration of 100 samples for certification as SRM's was accomplished by

direct comparison to Standard V1-G3 at 10-nanometer intervals over the wavelength

range 400 to 750 nanometers. Each sample was measured twice with the specular

component included and twice with the specular component excluded. The two

measurements were made for two orientations, rotating the sample 90 degrees in the

plane of the measured surface between measurements. The two measurements are then

averaged.

All of the reflectance measurements were made with the samples backed by

black felt. The reasons for using the black backing are related to the Vitrolite

translucency and will be discussed in more detail in a later section dealing with

this subject. (See a copy of the certificate in Appendix I.)

3
3. Using the Vitro! ite Reflectance Standard

The proper understanding of certain geometrical conditions affecting the

photometric accuracy of reflectance measurements in which Vitrolite is used as a working standard can help the user to avoid errors that may be introduced into his

measurements. These errors may result from a misunderstanding of the measuring

geometry for which the standard was calibrated or from a disregard for the restrictions imposed on the Vitrolite's use due to the inherent translucency of this

glass.

The Vitrolite reflectance standard has a fire polished surface which gives it

durability and stability. This polished surface reflects approximately four

percent of the incident light as specular reflection. The total 6-degree hemispherical reflectance of Vitrolite includes this specular component of reflected

light. If the Vitrolite is calibrated for the condition of illumination and

viewing in which the specular component is included, then this calibration data

should not be used if the Vitrolite is used in a geometry of illumination and

viewing where the specular component is excluded from the measurement. An example

of the latter condition would be a measurement of reflectance for a geometry in

which the Vitrolite is illuminated at an angle of incidence of 45 degrees from the

normal and viewed by the detector at the normal to the Vitrolite surface, or the reverse condition where the illumination is normal to the surface and the detector

views the Vitrolite at 45 degrees from the normal. If a reflectance standard is

to be used on an instrument using a 0°/45° or 45°/0° geometry, that reflectance

standard should be calibrated for these conditions of illumination and viewing.

Some integrating spheres have removable plugs which have been placed in the

sphere wall for the purpose of including or excluding the specular component of

the reflected light from the sample. The plug is usually filled with a white

material similar to the coating of the integrating sphere. This white plug is

used when making reflectance measurements with the specular component included.

It is replaced with a black plug or black cavity for making measurements with the

specular component excluded from the total reflected signal.

There are some important points to consider when using the black cavity for

the excluded specular mode of operation. The efficiency of the integrating sphere

changes when the white plug is replaced with a black cavity. This in itself would

not be a problem. However, the change usually affects the sample beam more than

it does the reference beam and results in a slight change in the balance between

the two beams. Because of this effect it is better to use a reflectance standard

which has been calibrated for the same geometry, particularly when making measurements with the specular component excluded. Because a Vitrolite calibration for

the excluded specular mode of measurement is so dependent on the sphere geometry,

it is difficult to use such a calibrated standard to obtain a proper calibration

unless the solid angle subtended by the specular light trap at the illuminated

area of the Vitrolite is the same for the integrating sphere on which it is used

as for the original calibration geometry. The assigned calibration data for the

excluded mode of measurement should only be used when the geometry of the integrating sphere is similar to that of the Hardy spectrophotometer on which the

standards were calibrated. The beam is incident on the Vitrolite at 6 degrees

from the normal and the light trap subtends a solid angle of 15 degrees at the

center of the illuminated area. It is recommended that a similar light trap be

placed in the specular position for the reference beam of the integrating sphere

when making measurements with the specular component of the Vitrolite excluded.

4
This is done to maintain the same balance between sample and reference beams. The

effects of the use of one or two light traps in an integrating sphere of the type

used in a Hardy spectrophotometer is outlined in figure 1. Figure 1 is included

in this discussion in order to illustrate what has come to be known over the years

as the "one black port versus the two black port" argument or problem.

In figure 1 there are six cross-sectional views of an integrating sphere of

the type used in a Hardy spectrophotometer. Each of these cross sections depicts

the path of the sample and reference beam, the sample and reference ports, and the

removable plugs for excluding the specular component of the reflected beams. The

six geometries illustrated in figure 1 show the effect of using one black cavity

or two black cavities when making measurements of the reflectance of an opal

glass. This white opal glass has been finely ground to provide a diffusely

reflecting surface. In figure 1-A two magnesium oxide targets are used to balance

the sample and reference at 100 percent. Note that these measurements date back

to an earlier time when smoked MgO was used to coat the measuring integrating

sphere and the reference target of the ref lectometer. These two targets have the same reflectance and give a reflectance value of 1.000 when the photometric scale

is adjusted to record this value. They are shown to be the same by measuring

them, interchanging them, and repeating the measurement. In figure 1-B the opal

glass has been placed in the sample beam. Its reflectance relative to the magnesium oxide reference target is 0.986 with the specular component included in the

total reflected signal. Placing a black cavity light trap in the sphere wall

(figure 1-C) at the angle of specular reflection for the opal glass results in a reflectance value of 0.980. This is 0.006 less than the reflectance of the opal

glass with the specular component included and might lead to the conclusion that

the opal glass has a specular component of 0.006. However, the same difference

can be obtained with a magnesium oxide target as can be seen in figure 1-D where

the magnesium oxide target is 0.994 or 0.006 less than the 1.000 value found for

the geometry illustrated in figure 1-A. Placing a second black cavity in the

sphere wall at the angle of specular reflection for the reference beam as shown in

figure 1-E results in a reflectance value of 1.000 for the magnesium oxide sample.

The reflectance value for the opal glass is 0.986 when measured with two black

cavities as shown in figure 1-F. This is the same value as was found for the opal

glass with the specular component included. The difference in the values of

reflectance obtained with one black cavity versus two black cavities for both the

magnesium oxide and the opal glass is 0.006. The following results are obtained

for the reflectance of Vitrolite relative to a magnesium oxide reference beam

target at 550 nanometers.

(a) Vitrolite, included (two white plugs) = 0.929

(b) Vitrolite, excluded (one black cavity) = 0.888

(c) Vitrolite, excluded (two black cavities) = 0.894

Again, the difference between the values of reflectance of Vitrolite with one black cavity versus two black cavities is 0.006. This difference of 0.006 occurs

for measurements of reflectance of the magnesium oxide, opal glass, and for the

Vitrolite. This is a common difference that appears related to the geometry of

the sphere rather than a property of the materials being measured. If the assumption is made that magnesium oxide is a nearly perfect diffuser, having no specular

component, then the results obtained with one black cavity as shown for the sphere

configuration illustrated in figure 1-D must be incorrect because the results of

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this measurement are 0.006 less than those obtained with a white plug (figure

1-A). Placing a second black cavity in the sphere does not reduce the reflectance

of the magnesium oxide by an additional 0.006 but restores the value to 1.000,

which is the same as was originally set for the configuration illustrated in

figure 1-A. When one side of the sphere is geometrically different from the

other, as is the case when a black cavity is placed in only one side of the sphere,

the detector does not sense the sample and reference beams as being equal even though the targets for these two beams are equal in reflectance. The important

point to remember is that when making reflectance measurements with the specular

component excluded, the 100 percent line values should be set with two black

cavities, and the Vitrolite standard and the samples should also be measured with

two black cavities because the standard values for the reflectance of the Vitrolite

for the specular excluded mode of operation were derived for this sphere configuration. The Vitrolite calibration for excluded specular component may not be valid

for use on integrating spheres in which the specular component is excluded by a geometry differing from the one illustrated in figure 1-F.

The preceding logic clearly makes a good argument in favor of using the two

black ports to make measurements of spectral reflectance with the specular com- ponent of sample reflectance excluded from the measurement. However, further

consideration of the information illustrated in figure 1 will show that it is

possible to obtain the correct reflectance in the excluded mode by using only one black cavity on the sample beam side of the integrating sphere if the substitutional method is used. If the reflectance value shown in figure 1-C is divided by

the reflectance value shown in figure 1-D, one obtains the following:

Reflectance of opal glass = .980/. 994 = .986

(using one black cavity).

The calculated reflectance is the same as the measured reflectance obtained with

two black cavities as shown in figure 1-F. The point to remember is that the

correct reflectance for the excluded specular component mode of measurement can be

obtained using one black port or two black ports if the correct procedures are followed. In summary the correct and incorrect procedures are:

Excluded Specular Component (using one black port)

The correct procedure for using one black port on the sample

side is to set the 100 percent value to read 1.000 with the

black cavity in place on the sample side, then substitute

the sample for the white diffuser used to set the 100 percent value.

Excluded Specular Component (using two black ports)

The correct procedure for using two black ports is to set

the 100 percent value as shown in figure 1-E, then substitute the sample for the white diffuser as shown in figure

1-F.

Incorrect Method (using one black port)

The incorrect procedure for measuring in the excluded mode

is to set the 100 percent value as shown in figure 1-A and

then make a measurement as shown in figure 1-C.

7
It is important to remember that double-beam instruments such as the Hardy

type integrating sphere illustrated in figure 1 are ratio-recording spectrophotometers and the values of reflectance obtained with such instruments are relative

and not absolute. That is they are relative to the reflectance of whatever white

diffuser is used to set the 100 percent value of the photometric scale. The

Vitrolite reflectance standard is assigned absolute reflectance values so that the user can adjust his relative measurements to a common absolute scale, regardless

of the reflectance of white diffusers used to balance the two beams of the spectrophotometer. The two white diffusers used to set the 100 percent value can be any

reasonably white, diffuse reflecting surfaces. They should be of approximately

equal reflectance. The Vitrolite reflectance standard is assigned absolute

reflectance values that can be used to adjust the reflectance values of any diffusely reflecting sample to the same absolute reflectance scale. The ratio of the

absolute reflectance of the Vitrolite standard to the measured reflectance of the

standard, multiplied by the measured reflectance of a test sample will adjust the

reflectance values of the test sample to the absolute reflectance scale of the

Vitrolite standard. This adjustment to the absolute scale will not correct for errors such as incorrect zero calibration or nonlinearity of the photometric

seal e.

4. Vitrolite Translucency

Vitrolite is an opal glass in which the incident light is scattered internally by body scattering rather than by surface scattering. Body scattering

provides a more uniform scattering or diffusion than surface scattering. However,

the translucency associated with Vitrolite may introduce some problems when using

it as a reflectance standard. The principal problem with the Vitrolite is the

loss of a portion of the incident light beam due to diffusion of the light out the

back, the edges, or behind the integrating sphere sample port edge. Improper use of the Vitrolite reflectance standard with respect to these translucency effects

will result in errors in the photometric accuracy of the reflectance measurements.

A detailed analysis of Vitrolite translucency was carried out at NBS in order

to determine the geometrical conditions and parameters within which Vitrolite can

be used as a reflectance standard without encountering errors due to its translucency. This study was performed through the use of the NBS Reference hazemeter

[5]. This instrument is well suited for experiments involving scattering and

translucency. It has a collimated light beam having a color temperature of approximately 6800 K (CIE Source C). The beam diameter can be varied. The integrating

sphere can be used for transmission or reflection. The sample port diameter is

also variable. The detector is equipped with a visual response filter giving the

hazemeter a peak response near 550 nanometers.

The Vitrolite used in the translucency study was prepared by grinding five

samples of the original stock to thicknesses of 2, 4, 6, 8, and 10 mm. The samples were ground to these thicknesses by removing glass from the back surface, leaving

the fire-polished front surface in its original condition. These five samples were 100 x 100 mm in area.

Figure 2 shows the diffuse transmission density (negative logarithm of transmittance, - log T) for thicknesses varying from 2 mm to 20 mm. The data curve in

figure 2 clearly shows that Vitrolite transmits approximately 10 percent (density

1.0) for a sample thickness of about 5 mm, 3 percent (density 1.5) for a thickness

of about 10 mm, and 1 percent (density 2.0) for a sample of 18 mm thickness.

8
Figure 2. The diffuse transmi ttance (plotted on an optical

density scale) to illustrate the linearity of

diffuse transmi ttance as a function of the

Vitro! ite thickness. The data were obtained by means of the NBS hazemeter. This instrument has

a visual response detector system with a peak

response near 550 nanometers.

9
Since the thickest sample was 10 mm, it was necessary to combine two or three

samples in order to obtain the diffuse transmission density of the thicknesses

between 10 mm and 20 mm. For these measurements the Vitrolite samples were optically coupled by a thin film of water to reduce interface reflections. The

combinations used for these measurements were: 10+2=12 mm, 10 + 4 = 14 mm,

10 + 6 = 16 mm, 10 + 8 = 18 mm, and 10 + 8 + 2 = 20 mm thickness.

Figure 3 shows the diffuse reflectance with the different Vitrolite thicknesses

backed by a white backing of approximately 99 percent reflectance and again with a black backing of less than 1 percent reflectance. In this case the light beam was incident on the Vitrolite normal to the surface so that the specular component was reflected back through the entrance port of the hazemeter integrating sphere and

excluded from the measurement.

The data curves in figure 3 show that the Vitrolite would have to be nearly

20 mm in thickness for its reflectance to be independent of the reflectance of the

backing material. Since the Vitrolite stock is approximately 10 mm in thickness,

it can be seen from the data shown in figure 3 that when using it as a reflectance

standard, the backing must be specified. At 10 mm thickness the Vitrolite reflectance can vary by as much as 1 percent depending on the reflectance of the backing.

For this reason all Vitrolite standards are calibrated with a black backing of less

than 1 percent reflectance. A black felt covered plate is provided with each SRM

Vitrolite standard for use as a backing.

The other important factor a user must be aware of when using Vitrolite as a reflectance standard is the problem of translucency effects where the incident

light beam diffuses through the Vitrolite and escapes through the edge of the

Vitrolite or gets trapped behind the edge of the sample port against which the

Vitrolite is mounted. Figures 4, 5, and 6 show how these edge losses due to

translucency are related to the Vitrolite thickness, incident light beam diameter,

and port diameter. In all three of these figures the Vitrolite reflectance is

shown for varying thicknesses and for white and black backings. Figure 4 shows the

edge loss effects for a large 100 mm x 100 mm Vitrolite on a 40 mm diameter port.

Figure 5 shows the same relationships with the port diameter increased to 60 mm.

In figure 6 the Vitrolite diameter was 42 mm and the port diameter was 40 mm. Here

the edge losses are greatest as would be expected while in figure 5 where the port

diameter was much greater, there is no indication of light loss for any Vitrolite

thickness or beam diameter since the largest beam diameter was 38 mm and not large

enough to approach the edge of the 60-mm diameter port to a point where losses

would occur.

The results of these translucency studies are summarized in figure 7 so that

the user can quickly determine whether or not the geometrical conditions under

which he is using the Vitrolite reflectance standard will introduce errors in his

calibration because of these translucency errors. In figure 7 the percentage of

the incident beam striking the Vitrolite standard that is lost from the measurement

because of edge losses is plotted as a function of the ratio of the beam diameter

to the port diameter. This ratio is only shown for Vitrolite of 10 mm thickness

since this is the approximate thickness of these standards. Two curves are shown.

The "worst case" for edge losses is shown by the curve labeled "Vitrolite (1.05 x diameter of port)". Here the Vitrolite is almost the same diameter as the port.

In this case the beam diameter must be less than 15 percent of the port diameter in

order to avoid edge losses. The other curve shows the edge losses for a Vitrolite

having a diameter "2.5 x diameter of port". With this size Vitrolite the beam

10
1.00

VITROLITE TRANSLUCENCY (550nm)

O WHITE BACKING ( ~ 99 %)

# BLACK BACKING ( < I %)

.95

.90

.85

.80

.75 8 10 12 THICKNESS (MM)

14 16

Figure 3. The reflectance of Vitrolite as a function of thickness

for Vitrolite backed by a white backing of approximately

99 percent reflectance and for Vitrolite backed by a black backing of less than one percent reflectance. The

data were obtained by means of the NBS hazemeter. This

instrument has a visual response detector system with a peak response near 550 nanometers.

11
1.00

2

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VITROLITE TRANSLUCENCY ( 550 NM ) 100 MM X I00MM ON 40MM DIAMETER PORT

O WHITE BACKING ( ~ 99%)

# BLACK BACKING ( < 1%)

.80

.7 5 1

10 14 18 22 26 30

BEAM DIAMETER (MM)

34 38 40

Figure 4. The reflectance of Vitrolite can be influenced by the

backing, Vitrolite thickness, size of the Vitrolite,

and size of the integrating sphere port on which the

Vitrolite is mounted. The data in figure 4 should be

compared with the data illustrated in figures 5 and 6

where the port size and Vitrolite size are changed.

The data were obtained-by means of the NBS hazemeter.

This instrument has a visual response detector system

with a peak response near 550 nanometers.

12
1.00

u

z

o

Q.so

o

cr<

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Ll) CL

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VITROLITE TRANSLUCENCY (550TM)

100 MM X 100 MM ON 60 MM DIAMETER PORT O WHITE BACKING (~99%)

$ BLACK BACKING ( < I %

)

[/) COUJ2

O

x

.80

.75 '

1 1 '

1

'

1 1 ' 6 10 14 18 22 2 6 30 34 38 40

BEAM DIAMETER (MM)

Figure 5. The reflectance of Vitrolite can be influenced by the

backing, Vitrolite thickness, size of the Vitrolite,

and size of the integrating sphere port on which the

Vitrolite is mounted. The data in figure 5 should be

compared with the data illustrated in figures 4 and 6

where the port size and Vitrolite size are changed.

The data were obtained by means of the NBS hazemeter.

This instrument has a visual response detector system

with a peak response near 550 nanometers.

13
1.00

VITROLITE TRANSLUCENCY (550nm)

42 MM DIAMETER ON 40 MM DIAMETER PORT

O WHITE BACKING ( — 99%)

# BLACK BACKING ( < 1%)

.95

o

0.o

o

o d

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.90

.80

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10 14 18 22 26 30

BEAM DIAMETER (MM)

34 38 40

Figure 6. The reflectance of Vitrolite can be influenced by the

backing, Vitrolite thickness, size of the Vitrolite,

and size of the integrating sphere port on which the

Vitrolite is mounted. The data in figure 6 should be

compared with the data illustrated in figures 4 and 5 where the port size and Vitrolite size are changed.

The data were obtained by means of the NBS hazemeter.

This instrument has a visual response detector system

with a peak response near 550 nanometers.

14
VITROLITE TRANSLUCENCY (550nm)

LOSS OF LIGHT DUE TO TRANSLUCENCY

RATIO : BEAM DIAMETER / PORT DIAMETER

Figure 7. The percentage of incident light beam that is lost out the

edge of the Vitrolite near the edge of the integrating sphere

post. The data were obtained for a Vitrolite of 1 0 mm thickness. The light lost from the measurement is due to the

Vitrolite transl ucency . The amount of light lost depends on the dimensions of the Vitrolite and the ratio of the sample

beam diameter to the port diameter. The data were obtained

by means of the NBS hazemeter. This instrument has a visual

response detector system with a peak response near 550 nanometers.

15
I diameter should not be greater than 50 percent of the port diameter in order to

avoid edge losses. The data shown in figure 7 should not be used as a correction

factor but only as a guideline to point out possible instrumental problems related

to transl ucency.

In summary it is clearly shown in figure 7 that edge loss errors can be

greater than 1 percent if the Vitrolite is illuminated with a beam having a diameter nearly the same as the port diameter. Therefore, the user should make certain

that the beam diameter is small enough in relation to the port diameter to avoid

edge losses. The user should also make certain that the Vitrolite is covered

by draping an opaque cloth over it to prevent room light from diffusing in through

the Vitrolite edges and into the integrating sphere. It is also important that the

Vitrolite be backed by the black felt-covered plate supplied with each standard.

The results of the translucency studies shown in figures 2 through 7 are representative of what a user will encounter in using Vitrolite reflectance standards with integrating spheres having circular ports and sample beams that are collimated and circular. Obviously, there are integrating spheres with rectangular

ports or ports that are not circular and ref 1 ectometers that do not have collimated

circular beams. Where these geometrical conditions exist, it is still a good rule

to avoid illuminating the Vitrolite with a beam that is greater in width or height

than 50 percent of the port width or height. In ref 1 ectometers in which the sphere

is illuminated by an uncollimated source and the Vitrolite is diffusely illuminated, then viewed by some limiting aperture such as a monochromator slit, the

Vitrolite calibration is still valid as long as the viewed area of the Vitrolite is

in a central area of the port, not exceeding 50 percent of the port diameter.

5. Cleaning and Storing Vitrolite Reflectance Standards

Vitrolite can be cleaned with soap and water. Mild liquid soap or plain white

hand soap will do. After washing, the standard should be rinsed with warm water

and dried with a soft tissue or cotton cloth which is free of grit that might

scratch the surface. Never clean with strong detergents or solvents. These may

permanently alter the Vitrolite surface through repeated use. The best way to

store a Vitrolite reflectance standard is to place it in a desiccator or glass

container so that the standard reflecting surface is in contact with air only.

16
6. References

Vitro! ite is a trade name for an opal glass that was manufactured by the

Libby Owens Ford Glass Company.

Goebel , David G. ; Caldwell, B. Patrick; Hammond, Harry K. Ill;

Use of an auxiliary sphere with a spectrophotometer to obtain absolute

reflectance, J. Opt. Soc. Am. 56_, 783 (1 966).

Venable, William H. , Jr.; Hsia, Jack J.; Weidner, Victor R.

Development of an NBS reference spectrophotometer for diffuse

transmi ttance and reflectance, Nat. Bur. Stand. (U.S.) Tech Note 594-11,

October 1976. 47 pages.

Venable, William H. , Jr.; Hsia, Jack J.; Weidner, Victor R.

Establishing a scale of directional -hemispherical reflectance

factor I: The Van den Akker Method, J. Res. Nat. Bur. Stand. (U.S.)

82_, 1, p. 29 (July-August 1 977).

Weidner, Victor R. ; Hsia, Jack J.; NBS hazemeter, its development and

testing, Appl . Opt. 18_, 1619 (May 15, 1979).

17
U. S. Department of Commerce

Malcolm Baldnge

Secretary

Appendix I Rational ^mtnvc of ^tnndntd*

Certificate

Standard Reference Material 2015

White Opal Glass Diffuse Spectral Reflectance

Standard for the Visible Spectrum

V. R. Weidner

This Standard Reference Material (SRM) is intended for use in calibrating the photometric scale of integrating sphere

reflectometer-spectrophotometers used in the measurement of spectral 6°, hemispherical reflectance. SRM 20 15 is a

5.1 -cm x 3.8-cm, fire-polished, white opal glass (vitrolite).

This SRM was measured at 10-nm intervals from 400 to 750 nm. The certified values were determined in the following

way. The 6° hemispherical diffuse reflectance factor of a master plate was measured on the NBS High Accuracy

Reference Spectrophotometer for diffuse reflectance, using techniques for determining absolute reflectance values

(reflectance relative to a perfect diffuser). This master plate was then used to transfer the absolute reflectance scale to the

reflectance SRM through the use of a working plate and a high-precision recording spectrophotometer. The uncertainty

in the values of absolute diffuse reflectance assigned to the master plate is 0. 1 5 percent. The total uncertainty of the

certified values of absolute diffuse reflectance is ± 1.0 percent at the 95 percent confidence level, the certified values tor the "included specular component" are given in Table 1 . I) ncertified values for the "excluded specular component" are given for information only in Table 2. The white opal glass can be cleaned with a mild liquid soap and warm water, followed by a rinse in distilled water. The

fire-polished surface and the reflectance of the standard are very stable. However, care should be exercised in cleaning

and handling to avoid scratching the polished surface. The standard should be stored in a covered glass enclosure when

not in use.

This SRM is issued with a black felt covered aluminum plate. This black telt is to be placed against the back ol the SRM

when measuring its reflectance. The same black backing was used in calibrating the SRM at NBS. This white glass is translucent and may not be suitable as a reflectance standard for some reflectometers. The calibration of this dif fuse spectral reflectance standard was done in the Radiometric Physics Division of the Center

for Radiation Research at NBS.

The technical and support aspects involved in the certification and issuance of SRM 2015 was coordinated through the Office of Standard Reference Materials by R.K. Kirby.

National Burewu of Standard;.

Frnest Ambler. Director

Washington, D.C.

May 5, 1982

20234 George A. Uriano, Chief

Office of Standard Reference Materials

18
THIS IS A SAMPLE

G°/Hcun spherical Reflectance Factor (Relative to a Perfect Diffuser)

White Opal Glass Serial No. V6-G?Q01

TABLE 1 TABLE 2 Wavelength

( nrn ) INCLUDED SPECULAR COMPONENT EXCLUDED SPECULAR COMPONENT

400 0.905 0.864

410 .896 .857

420 ,892 .852

430 .892 .852

440 .890 .852

450 .898 .860

460 .908 .869

470 .911 .872

480 .911 .872

490 .915 .875

500 .916 .878

510 .919 .880

520 .921 .882

530 .922 .882

540 .922 .884

550 .922 .883

560 .922 .882

570 . 920 . 882

580 .918 .881

590 .916 .879

600 .914 .877

610 .913 .875

620 .910 .873

630 .908 .870

640 .906 .869

650 .906 .868

660 .905 .867

670 .903 .865

680 .904 .865

690 .902 .864

700 .901 .863

710 .899 .860

720 .897 .858

730 .894 .857

740 .892 .854

750 *S90 .853

19
U. S. Department of Commerce

Malcolm Baldrige

'Secretary Appendix II

Rational ^ttram of js»tantlartte

Certificate

Standard Reference Material 2016

White Opal Glass Diffuse Spectral Reflectance

Standard for the Visible Spectrum

V. R. Weidner

This Standard Reference Material (SRM) is intended for use in calibrating the photometric scale of integrating sphere

reflectometer-spectrophotometers used in the measurement of spectral 6° / hemispherical reflectance. SRM 20I6 is a 10-cm x 10-cm, fire-polished, white opal glass (vitrolite).

This SRM was measured at 10-nm intervals from 400 to 750 nm. The certified values were determined in the following

way. The 6° / hemispherical diffuse reflectance factor of a master plate was measured on the NBS High Accuracy

Reference Spectrophotometer for diffuse reflectance, using techniques for determining absolute reflectance values

(reflectance relative to a perfect diffuser). This master plate was then used to transfer the absolute reflectance scale to the

reflectance SRM through the use of a working plate and a high-precision recording spectrophotometer. The uncertainty

in the values of absolute diffuse reflectance assigned to the master plate is 0.15 percent. The total uncertainty of the

certified values of absolute diffuse reflectance is ± 1.0 percent at the 95 percent confidence level, the certified values for the "included specular component" are given in Table 1 . Uncertified values for the "excluded specular component" are given for information only in Table 2. The white opal glass can be cleaned with a mild liquid soap and warm water, followed by a rinse in distilled water. The

tire-polished surface and the reflectance of the standard are very stable. However, care should be exercised in cleaning

and handling to avoid scratching the polished surface. The standard should be stored in a covered glass enclosure when

not in use.

This SRM is issued with a black felt covered aluminum plate. This black felt is to be placed against the back of the SR M

when measuring its reflectance. The same black backing was used in calibrating the SRM at NBS. This white glass is translucent and may not be suitable as a reflectance standard for some reflectometers. The calibration of this diffuse spectral reflectance standard was done in the Radiometric Physics Division of the Center

for Radiation Research at NBS.

The technical and support aspects involved in the certification and issuance of SRM 2016 was coordinated through the Office of Standard Reference Materials by R.K.. Kirby.

National Buraau oT Slandards

Ernest Ambler. Director

Washington, D.C. 20234

May 5, 1982

20

George A. Uriano, Chief

Office of Standard Reference Materials
THIS IS A SAMPLE

6°/ttemisphcTical Reflectance Factor (Relative to a Perfect Diffuser)

White Opal Glass Serial No. V6-G4001

TABLE 1 TABLE 2

INCLUDED SPECULAR COMPONENT EXCLUDED SPECULAR COMPONENT

400 0.906 0.864

410 .896 .858

420 .892 .852

430 .892 .853

440 .890 .852

450 .899 .861

460 .908 .868

470 .911 .872

480 .911 .873

490 .914 .876

500 .916 .879

510 .919 .882

520 .922 .882

530 .923 .884

540 .922 .884

550 .922 .883

560 .922 .883

570 .921 .883

580 .918 .881

590 .916 .879

Wavelength

600

610

620

630

640

650

660

670

680

690

700

710

720

730

740.

750

.915

.913

.910

.907

.905

.905

.904

.903

.902

.901

.901

.898

.896

.894

.892

.890

.877

.875

.873

.870

.869

.868

.867

.866

.865

.864

.863

.862

.859

.857

.854

.852

21
NBS-1 14A « REV. 2-8C) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBS SP 260-82

2. Performing Organ. Report No 3. Publ ication Date April 1983

4. TITLE AND SUBTITLE

Standard Reference Materials:

White Opal Glass Diffuse Spectral Reflectance Standards for the Visible Spectrum

(SRM's 2015 and 2016)

5. AUTHOR(S)

Victor R. Weidner

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City. State, ZIP)

NBS Office of Standard Reference Materials

10. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 83-600516

JJ Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most si gnificant information. If document includes a significant

bibliography or literature survey, mention it here)

Vitrolite white opal glass has been calibrated for use as diffuse spectral

reflectance standards since 1944. Its uniformity and long-term durability make

it useful as an everyday working standard for spectrophotometry measurements in

the visible spectral range. However, its translucency can introduce some errors

in such measurements if improperly used. Prior to 1965 the Vitrolite reflectance

standards were issued with diffuse reflectance values relative to freshly smoked

magnesium oxide. Since that date the calibration of these standards is reported

on an absolute reflectance scale or one which is relative to a perfect diffuser.

Since the completion of the NBS Reference Spectrophotometer for diffuse reflectance measurements in 1975, work on the perfection of techniques for determining

a more accurate absolute reflectance scale has made it possible to further improve

these measurements. As a result of this effort, the Vitrolite reflectance standards

are now more accurately characterized and are being issued as a Standard Reference

Material

.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s)

diffuse; reflectance; spectrophotometry; standard; translucency; Vitrolite

13. AVAILABILITY

Unlimited

For Official Distribution. Do Not Release to NTIS

Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

33

15. Price

$3.75

USCOMM-DC 6043-P80

iz US. GOVERNMENT PRINTING OFFICE : 1983 O—380-997 (5032)


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