NATL INST. OF STAND & TECH

AlllOfc, 3t053fl

NBS SPECIAL PUBLICATION 260*41

Standard Reference Materials:

USE OF STANDARD LIGHT-SENSITIVE

PAPER FOR CALIBRATING CARBON

ARCS USED IN TESTING TEXTILES

FOR COLORFASTNESS TO LIGHT

National

Bureau f

Standards

ill
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 was established by an act of Congress 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 measure- ment 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 consists of the Institute for Basic Standards, the Institute for Materials

Research, the Institute for Applied Technology, the Center for Computer Sciences and

Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United States of a complete and consistent system of physical measurement; coordinates

that system with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of a Center for Radiation Research, an Office of Measurement Services and the following divisions: Applied Mathematics—Electricity—Heat—Mechanics—Optical Physics—Linac

Radiation2—Nuclear Radiation2—Applied Radiation2—Quantum Electronics3—

Electromagnetics3—Time and Frequency3 —Laboratory Astrophysics3 —Cryogenics3

. THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research lead- ing to improved methods of measurement, standards, and data on the properties of

well-characterized materials needed by industry, commerce, educational institutions, and

Government; provides advisory and research services to other Government agencies;

and develops, prbduces, and distributes standard reference materials. The Institute consists of the Office of Standard Reference Materials and the following divisions: Analytical Chemistry—Polymers—Metallurgy—Inorganic Materials—Reactor

Radiation—Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to pro- mote the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations leading to the development of technological standards (including mandatory safety standards), codes

and methods of test; and provides technical advice and services to Government agencies

upon request. The Institute also monitors NBS engineering standards activities and

provides liaison between NBS and national and international engineering standards

bodies. The Institute consists of the following divisions and offices: Engineering Standards Services—Weights and Measures—Invention and

Innovation—Product Evaluation Technology—Building Research—Electronic Technology—Technical Analysis—Measurement Engineering—Office of Fire Programs.

THE CENTER FOR COMPUTER SCIENCES AND TECHNOLOGY conducts re- search and provides technical services designed to aid Government agencies in improving cost effectiveness in the conduct of their programs through the selection, acquisition,

and effective utilization of automatic data processing equipment; and serves as the principal focus within the executive branch for the development of Federal standards for automatic data processing equipment, techniques, and computer languages. The Center

consists of the following offices and divisions: Information Processing Standards—Computer Information—Computer Services —Systems Development—Information Processing Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination

and accessibility of scientific information generated within NBS and other agencies of

the Federal Government; promotes the development of the National Standard Reference

Data System and a system of information analysis centers dealing with the broader

aspects of the National Measurement System; provides appropriate services to ensure

that the NBS staff has optimum accessibility to the scientific information of the world,

and directs the public information activities of the Bureau. The Office consists of the following organizational units: Office of Standard Reference Data—Office of Technical Information and

Publications—Library—Office of International Relations.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

2 Part of the Center for Radiation Research.

3 Located at Boulder, Colorado 80302.
lal Bureau of Standards DEC 1974

Standard Reference Materials:

n Use of Standard Light-Sensitive Paper

\ For Calibrating Carbon Arcs Used in

Testing Textiles For Colorfastness to Light

Lawrence A. Wood and Paul J. Shouse

Institute for Materials Research

National Bureau of Standards

• ' . Washington, D.C. 20234

U.S. DEPARTMENT OF COMMERCE, Peter G. Peterson, Secretary

NATIONAL BUREAU OF STANDARDS, Lawrence M. Kushner, Acting Director.,

Issued August 1972
Library of Congress Catalog Card Number: 7 2-600192

National Bureau of Standards Special Publication 260-41

Nat. Bur. Stand. (U.S.), Spec. Publ. 260-41, 24 pages (Aug. 1972)

CODEN: XNBSAV

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. 03.10:260-41). Price 30 cents.
PREFACE

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

National Bureau of Standards are "well-characterized materials, produced in quantity, that calibrate a measurement

system to assure compatability of measurement in 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. In many industries

traceability of their quality control process to the national

measurement system is 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 NBS in arriving

at the certified values of the SRM's produced. An NBS 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 all phases of the preparation, measurement,

and certification 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. It is also

hoped that these papers will 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 (s). 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

J. Paul Cali, Chief

Office of Standard Reference Materials
CONTENTS

PAGE

1. INTRODUCTION 1

2 . NBS MASTER LAMP 3

3. LIGHT-SENSITIVE PAPER 4

4. STANDARD FADING HOURS (SFH) 6

5. EFFECT OF DEVIATIONS FROM STANDARD CONDITIONS . . 7

5.1 BLACK-PANEL TEMPERATURE 7

5.2 HUMIDITY 8

5.3 INTERMITTENT EXPOSURE 9

6. PROCEDURE FOR EXPOSURE 9

7. RATING OF THE PAPERS AFTER EXPOSURE 10

7.1 VISUAL ESTIMATION

% 10

7.2 REFLECTANCE MEASUREMENTS 11

7.3 CALIBRATION BY OTHER PROPERTIES 13

8. FREQUENCY OF CALIBRATION 13

9. PROCEDURE FOR ORDERING PAPER AND BOOKLETS . . . . 15

10. REFERENCES 17

iv
OTHER NBS PUBLICATIONS IN THIS SERIES

NBS Spec. Publ. 260, Catalog of Standard

Reference Materials, July 1970. 75 cents.*

(Supersedes NBS Misc. Publ. 260, January 1968 and NBS Misc. Publ. 241,

.

March 1962.)

NBS Misc. Publ. 260-1, Standard Reference

Materials: Preparation of NBS White Cast

Iron Spectrochemical Standards, June 1964.

30 cents.*

NBS Misc. Publ. 260-2, Standard Reference

Materials: Preparation of NBS Copper-Base

Spectrochemical Standards, October 1964.

35 cents.*

NBS Misc. Publ. 260-3, Standard Reference

Materials: Metallographic Characterization of an NBS Spectrometric Low-Alloy Steel

Standard, October 1964. 20 cents.* (Out of

print).

NBS Misc. Publ. 2604, Standard Reference

Materials: Sources of Information on Standard Reference Materials, February 1965.

20 cents.* (Out of print).

NBS Misc. Publ. 260-5, Standard Reference

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

March 1965. 25 cents.* (Out of print).

NBS Misc. Publ. 260-6, Standard Reference

Materials: Methods for the Chemical Analysis

of White Cast Iron Standards, July 1965.

45 cents.*

NBS Misc. Publ. 260-7, Standard Reference

Materials: Methods for the Chemical Analysis

of NBS Copper-Base Spectrochemical Standards, October 1965. 60 cents.*

NBS Misc. Publ. 260-8, Standard Reference

Materials: Analysis of Uranium Concentrates

at the National Bureau of Standards, December 1965. 60 cents.* (Out of print).

NBS Misc. Publ. 260-9, 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, November

1965. 15 cents.*

NBS Misc. Publ. 260-10, Standard Reference

Materials: Homogeneity Characterization on NBS Spectrometric Standards II: Cartridge

Brass and Low-Alloy Steel, December 1965.

30 cents.*

NBS Misc. Publ. 260-11, Standard Reference

Materials: Viscosity of a Standard Lead-Silica

Glass, November 1966. 25 cents.*

NBS Misc. Publ. 260-12, Standard Reference

Materials: Homogeneity Characterization of

NBS Spectrometric Standards III : White Cast

Iron and Stainless Steel Powder Compact,

September 1966. 20 cents.*

NBS Misc. Publ. 260-13, Standard Reference

Materials: Mossbauer Spectroscopy Standard

for the Chemical Shift of Iron Compounds,

July 1967. 40 cents.*

NBS Misc. Publ. 260-14, Standard Reference

Materials: Determination of Oxygen in Fer- rous Materials - SRM 1090, 1091, and 1092,

September 1966. 30 cents.*

NBS Misc. Publ. 260-15, Standard Reference

Materials: Recommended Method of Use of

Standard Light-Sensitive Paper for Calibrating Carbon Arcs Used in Testing Textiles for

Colorfastness to Light, June 1967. 20 cents.*

NBS Spec. Publ. 260-16, Standard Reference

Materials: Homogeneity Characterization of

NBS Spectrometric Standards IV: Preparation and Microprobe Characterization of

W-20% Mo Alloy Fabricated by Powder

Metallurgical Methods, January 1969.

35 cents.*

NBS Spec. Publ. 260-17, Standard Reference

Materials: Boric Acid; Isotopic and Assay

Standard Reference Materials, February

1970. 65 cents.*

NBS Spec. Publ. 260-18, Standard Reference

Materials: Calibration of NBS Secondary

Standard Magnetic Tape (Computer Amplitude Reference) Using the Reference Tape

Amplitude Measurement "Process A", November 1969. 50 cents.*

NBS Spec. Publ. 260-19, Standard Reference

Materials: Analysis of Interlaboratory Measurements on the Vapor Pressure of Gold

(Certification of Standard Reference Material

745), January 1970. 30 cents.*

NBS Spec. Publ. 260-20, Standard Reference

Materials: Preparation and Analysis of Trace

Element Glass Standards. (In preparation)

NBS Spec. Publ. 260-21, Standard Reference

Materials: Analysis of Interlaboratory Measurements on the Vapor Pressures of Cadmium and Silver, January 1971. 35 cents.*

NBS Spec. Publ. 260-22, Standard Reference

Materials: Homogeneity Characterization of

Fe-3Si Alloy, February 1971. 35 cents.*

NBS Spec. Publ. 260-23, Standard Reference

Materials: Viscosity of a Standard Borosili- cate Glass, December 1970. 25 cents.*
NBS Spec. Publ. 260-24, Standard Reference

Materials: Comparison of Redox Standards,

January 1972. $1.*

NBS Spec. Publ. 260-25, Standard Reference

Materials: A Standard Reference Material

Containing Nominally Four Percent Austenite, February 1971. 30 cents.* NBS Spec. Publ. 260-26, Standard Reference

Materials: National Bureau of Standards—

U.S. Steel Corporation Joint Program for

Determining Oxygen and Nitrogen in Steel,

February 1971. 50 cents.* NBS Spec. Publ. 260-27, Standard Reference

Materials: Uranium Isotopic Standard Refer- ence Materials, April 1971. $1.25.*

NBS Spec. Publ. 260-28, Standard Reference

Materials: Preparation and Evaluation of

SRM's 481 and 482 Gold-Silver and GoldCopper Alloys for Microanalysis, August

1971. $1.*

NBS Spec. Publ. 260-29, Standard Reference

Materials: Calibration of NBS Secondary

Standard Magnetic Tape (Computer Amplitude Reference) Using the Reference Tape

Amplitude Measurement "Process A-Model

2", June 1971.60 cents.* NBS Spec. Publ. 260-30, Standard Reference

Materials: Standard Samples Issued in the

USSR (A Translation from the Russian),

June 1971. $1.*

NBS Spec. Publ. 260-31, Standard Reference

Materials: Thermal Conductivity of Electrolytic Iron SRM 734 from 4 to 300 K,

November 1971. 35 cents.* NBS Spec. Publ. 260-32, Standard Reference

Materials: The Cooperative Study of Temperature Scale Standards for DTA by ICTA and

NBS. (In preparation)

NBS Spec. Publ. 260-33, Standard Reference

Materials: Comparison of Original and Supplemental SRM 705, Narrow Molecular

Weight Distribution Polystyrene, H. L. Wagner, May 1972. 35 cents.* NBS Spec. Publ. 260-34, Standard Reference

Materials: Thermoelectric Voltage, April

1972. 40 cents.* NBS Spec. Publ. 260-35, Standard Reference

Materials: Thermal Conductivity of Austenitic Stainless Steel, SRM 735 from 5 to 280 K, April 1972. 35 cents.* NBS Spec. Publ. 260-36, Standard Reference

Materials: A Referee Method for the Deter- mination of Calcium in Serum. SRM 736,

May 1972. $1.25.*

NBS Spec. Publ. 260-37, Standard Reference

Materials: Methods of Analysis of NBS Clay

Standards, June 1972. 75 cents.* NBS Spec. Publ. 260-38, Standard Reference

Materials: Preparation and Calibration of

Standards of Spectral Specular Reflectance,

May 1972. 60 cents.* NBS Spec, Publ. 260-39, Standard Reference

Materials: The Eddy Current Decay Method

for Resistivity Characterization of HighPurity Metals, May 1972. 55 cents.* NBS Spec. Publ. 260-40, Standard Reference

Materials: Selection of Thermal Analysis

Temperature Standards Through a Cooperative Study (SRM 758, 759, 760). (In preparation)

NBS Spec. Publ. 260-41, Standard Reference

Materials: Use of Standard Light-Sensitive

Paper for Calibrating Carbon Arcs used in Testing Textiles for Colorfastness to Light.

(In preparation)

*Send order with remittance to: Superintendent of Documents, U.S. Government Printing Office,

Washington, D.C. 20402. Remittance from foreign countries should include an additional

one-fourth of the purchase price for postage.
USE OF STANDARD LIGHT-SENSITIVE PAPER FOR CALIBRATING

CARBON ARCS USED IN TESTING TEXTILES FOR

COLORFASTNESS TO LIGHT

by

Lawrence A. Wood and Paul J. Shouse

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

The use of NBS Light-Sensitive Paper and NBS

Booklets of Standard Faded Strips in the

standardization of carbon arcs is described.

These lamps are used to determine the fading

characteristics and degradation of textiles

and other materials when subjected to visible

and ultraviolet radiation. The light-sensitive

paper is useful in calibrating the arcs in terms

of NBS Standard Fading Hours (SFH) or equivalent

exposure in the NBS Master Carbon-Arc Lamp.

Key words: Carbon-arcs, standardization of; color-fastness,

testing of; fading tests, standardization; light-sensitive

paper; paper, light-sensitive; textiles, fading of.

1 . INTRODUCTION

Carbon-arc lamps are widely used for testing colorfastness and stability of materials to visible and ultraviolet

radiation. The variability of the output of a given lamp

and the differences between lamps have led to the extensive

use of standard reference materials that undergo measurable

changes when exposed to this radiation.

The American Association of Textile Chemists and Colorists, following work begun in 1931 or earlier, developed a

set of 8 blue wool standards covering various ranges up to

640 hours of exposure. The steps are logarithmic, each standard requiring approximately twice the exposure of the previous

one to obtain equivalent fading. These are in extensive

use in testing the fading of textiles. One of these,

denoted as L-4, has been the subject of a detailed study

1
[1] which showed that for carbon-arc exposures near 20 hours

the standard deviation of a single instrumental measurement

of color difference corresponded to about 3 Standard Fading

Hours (SFH) . A group of 9 observations near 20 SFH would

then be expected to range from 15.5 to 24.5 SFH, since

statistical theory predicts that the range is approximately

the product of the standard deviation by the square root

of the number of observations. This precision is adequate

for its intended purpose of placing an unknown specimen in

the proper step of the 8-step logarithmic scale of exposures,

but is not good enough to serve as a basis for calibrating

and adjusting the arcs.

Consequently the National Bureau of Standards , following

research work begun about 19 40 [2] , developed and issued

standard light sensitive ~paper, for which during a given

exposure the change in spectral reflectance (at various

wavelengths) is from 10-20 times that of the wool [1] and

the change in luminous reflectance, or tristimulus Y value,

is 15-20 times that of the wool. The precision of determination of exposure is found to be about 4-fold better than

that with the wool. A group of 9 observations on the paper

near 20 SFH is expected to range from about 18.8 to 21.2

SFH. The period of 20-24 hours is particularly important

because it corresponds approximately to the life of one

set of carbons

.

In calibrating a given carbon arc the paper is exposed

and then compared with six strips of the paper which have

been exposed for different known periods of time in the NBS

Master Carbon-Arc Lamp. The calibration procedure outlined

below is the same as that currently specified in Appendix B

of AATCC Test Method 16A-19 71 (Technical Manual, American

Association of Textile Chemists and Colorists, P.O. Box

12215, Research Triangle Park, North Carolina 27709).

2
2. NBS MASTER LAMP

The present NBS Master Lamp is an Atlas Electric

Device type SMC-R enclosed carbon-arc Fade-Ometer operated

on alternating current.* The arc voltage is 120-145 V and

the current 15-17 A (ranges specified by the manufacturer)

.

The construction of the unit is almost identical with that

of the Fade-Ometer described in detail by Boor and

Trucker [3] . It uses No. 70 solid carbons and No. 20 cored

carbons . The solid carbon is placed in the upper holder

and the cored carbon in the lower holder for one run, and

these positions are reversed for the next run. The arc is

enclosed in a special Pyrex glass globe (No. 9200PX)

.

The specimems are exposed (without backing) in a rack

20 in. (50.8 cm) in diameter rotating at 3 rpm.

* Footnote : Manufactured by Atlas Electric Devices Co., 4114 N.

Ravenswood Avenue, Chicago, Illinois 60613.

Certain commercial equipment and instruments are

identified here and elsewhere in this publication in order

to adequately specify the experimental procedure. In no

case does such identification imply recommendation or

endorsement by the National Bureau of Standards, nor does

it imply that the equipment or instruments identified are

necessarily the best available for the purpose.

3
I A black panel of enameled metal is placed in one of the

specimen positions in the rack. The black-panel temperature

is held at 150 ± 5°F (65.6 ± 2°C) by dampers which automatically control the ratio of exit air to recirculated

air. The control element for the dampers is in the stream

of humidified inlet air and is manually set to maintain

the black-panel temperature. It should be noted that

the American Association of Textile Chemists and Colorists

specifies a black-panel temperature of 145 ± 5°F (63 ± 3°C)

in AATCC Test Method 16A-19 71.

The variation during a single run seldom exceeds ±4°F.

The ambient temperature (77°F, 25°C) and humidity (45% RH,

Dew Point 54°F, 12°C) and size of our present laboratory

are such that under these conditions the temperature of the

exit air is usually 118 ± 2°F (47.8 ± 1°C) . Moisture is added to the circulating air by water sprayed

from a rotating disk to raise the relative humidity of the

exit air to 30% at the dry-bulb temperature of 118°F. A

bimetallic thermostat responding to wet-bulb temperature

starts and stops the rotating disk. The humidity is controlled by automatically maintaining the wet-bulb temperature

at a desired value (88°F, 31°C in the present instance).

The dew-point of the exit air under these conditions

is 79 °F (26 °C) . It would be quite inconvenient to maintain a higher humidity, since a dew point higher than room

temperature gives rise to condensation difficulties when

the air is allowed to cool from 118°F to room temperature.

3. LIGHT- SENSITIVE PAPER

Successive lots of light-sensitive paper have been

issued by the National Bureau of Standards since about

1945 12] . They are now sold as items in the NBS Standard

Reference Materials program and carry the designations SRM

700 for the unexposed paper and SRM 701 for the booklets

4
of six strips which have been exposed for stated periods

of time in the NBS Master Lamp. The particular lot

is designated by a letter following the SRM number. Thus,

SRM 700a and SRM 701a were issued in June 196 5, and were

followed by SRM 700b and SRM 701b in June 19 67. The most

recent lot is SRM 700c and SRM 701c, issued in November 1971.

Lots differ slightly both in the reflectance of the unexposed

paper and in the rate of fading. Consequently the paper from

a given lot can be used only with the booklet from the same

lot. Each order of booklet and package of paper is accompanied

by a Certificate of Calibration including the numerical values

characteristic of the particular lot.

The paper, made in the National Bureau of Standards

paper mill, contains the direct azo dye Benzo Azurine G,

Colour Index Direct Blue [eight] No. 24140. The unexposed

paper is supplied in pieces 2-5/8 by 3-1/4 inches. Each

booklet contains 6 paper strips (about 1-1/2 by 3 inches)

which have been faded by exposure for different times in the

NBS Master Carbon Arc described in the preceding section.

To facilitate production the booklets are assembled in four

different series with the following nominal values

and

Series A - 6, 8, 10, 14, 18, and 22SFH

Series B - 7

,

9, 11, 15, 19, and 23SFH

Series C - 8, 10, 12, 16, 20, and 24SFH

Series D - 9, 11, 13, 17, 21, and 25SFH

The different series have the same-sized intervals, and the

booklets of each series are fully equivalent to each other.

5
4. STANDARD FADING HOURS (SFH)

The quantitative basis for establishing a unit standard

fading hour (SFH) at the National Bureau of Standards before

1950 has been discussed in detail in a previous publication

[1] . A "Fade-Ometer Hour" had already been used for some

years in the textile industry, and 20 SFH was defined as

being equivalent to 20 clock hours (CH) of exposure in the

Atlas Type FDA-R Carbon-Arc Fade-Ometer, the type in most

general use at the time. Since February 19 49 , every effort

has been made by repeated comparisons involving lightsensitive paper to keep constant the dosage of carbon arc

radiation represented by 20 SFH.

In order to attain this aim, over the years repeated

observations have been made of the color changes found

in a given lot of paper for 20 hours of operation of the

NBS Master Carbon-Arc Lamp. No significant differences

have been found. Each new lot of paper has been compared

carefully with one or more of the preceding lots at the

time it has been introduced. The exposures of the new lot

have been expressed in terms of the SFH defined by the

preceding lots

.

Over the years the conditions of operation of the master

carbon-arc lamp have been controlled and specified with

progressively increasing detail and some changes in the

arc have been made. As a result, it is found that a 20-hour

exposure in the present NBS Master Lamp under the conditions

of operation given above causes fading of the ligh-sensitive

paper by an amount equivalent to about 18 SFH.

Defining a severity factor F as the ratio of standard

fading hours SFH to clock hours CH, one finds that F for the

NBS Master Lamp is about 0.9 at 20 CH. It is possible to

vary the severity factor for the carbon arc somewhat by

changing the arc voltage by using a different transformer

6
tap, but only a limited range of adjustment is possible.

The severity factor can be altered markedly by deviations

from the standard conditions of specimen distance, humidity,

and black-panel temperatures. It should be kept in the

range 0.9 ± 0.1 at 20 CH. The severity factor generally

decreases with decreasing exposure time. The severity is

obviously lower than that employed prior to 19 50 (when

F_ = 1.0). The reduction is probably due chiefly to the

lowering of the recommended effective black-panel

temperature from its early value of about 165°F (73.9°C)

to 150°F (65.6°C)

.

5. EFFECT OF DEVIATIONS FROM STANDARD CONDITIONS

In calibrations at the National Bureau of Standards

all work is done under the standard conditions already

described. It is of interest to examine the effects of

several deviations from these standard conditions.

5.1 BLACK-PANEL TEMPERATURE

A recent unpublished NBS study of the fading of the

paper at lower black-panel temperatures (while maintaining

30% RH for the exit air) shows a reduction in the number

of SFH at the rate of about 0.3 SFH for each Fahrenheit

degree. Thus if a 20-hour exposure gives 18 SFH at 150F,

about 16.5 SFH will be found at 145°F and about 12.9 SFH at

133°F. The corresponding severity factors are 0.9, 0.83,

and 0.65, respectively. The last temperature (133°F, 56.1°C)

is the lowest black-panel temperature attainable without

increasing the cooling facilities in the room where our arc

is located.

Similar observations regarding the effect of temperature

on the fading of NBS Light-Sensitive Paper Lot 1554 were

reported by Boor and Trucker I 3J

.

7
5.2 HUMIDITY

In the NBS Master Lamp the relative humidity is maintained at 30% at the temperature of the exit air, usually

about 118°F. This is accomplished by adding moisture to

the air passing over the specimens. It has been pointed

out that the dew point is an important parameter in these

considerations [4] . The dew point under these conditions

is about 79 °F. Reported values of dew point and relative

humidity appreciably higher than those just mentioned are

questionable, because measurement inaccuracies almost

always lead to spuriously high values of humidity. Furthermore, if no condensation is observed as the exit air cools to

room temperature, the dew point must be below room temperature. On the other hand, if condensation is observed, the

presence of liquid water droplets can cause serious experimental difficulties.

If the lamp does not have provision for adding moisture,

the dew point of the air around the specimens will be

approximately the same as that of the laboratory. Unless

the laboratory humidity is controlled, the dew point may

vary from a maximum of perhaps 79 °F on a very humid summer

day to 10 °F or less during the winter. The corresponding

range of relative humidity when the air is heated to 118°F

without the addition of moisture is from 30% to about 2%.

The fading of the paper, as well as that of most textiles,

is considerably reduced as the humidity is lowered below

the standard condition of 30% at exit-air temperature. Some

indication of the magnitude of this effect can be noted from

the results of Boor and Trucker [3] on paper from Lot 1554.

The reduction in fading is particularly great when the

relative humidity falls below 20%.

8
5.3 INTERMITTENT EXPOSURE

The light-sensitive paper, as well as many textiles,

fades more in a given time if exposed intermittently than

if exposed continuously, probably because of an increase in

relative humidity of the air and moisture content of the

paper while the lamp is shut off, with more rapid fading

when it is first turned on again. It is therefore necessary

to begin tests with a fresh set of carbons in the lamp and

to avoid shut-downs

.

6. PROCEDURE FOR EXPOSURE

Mount a piece of unexposed light-sensitive paper in a

specimen holder of the lamp without backing and place it

in the lamp at the time it is started. The side of the

paper facing the arc should be the one containing no

printing. Furthermore, the paper should be placed so that

the printed matter is not immediately back of the portion

of the strip which is being exposed. Vacant positions in

the specimen holder should be filled with dummy specimens

to reduce variations in reflections and air currents.

At the end of the run remove the strip and allow it to

stand in the dark at room temperature for at least 2 hours

in order for it to cool and to regain its normal moisture

from the air. If the fading is to be judged only visually,

trim off and discard the unexposed edges of the paper and

of the strips in the booklets as they may affect the judgment

of the fading. For instrumental measurements the edges

should remain attached for enhanced ease of handling during

the measurements

.

9
7. RATING OF THE PAPERS AFTER EXPOSURE . 7.1 Visual Estimation

Trim off and discard the unexposed edges of the paper,

as already mentioned, so that the exposed paper may be

placed immediately adjacent to the standard faded strips in

the booklet. To make a visual comparison, hold the booklet

in one hand, allow the pages to flip open one after another,

rear cover first, and slip the exposed paper under one

standard faded strip after another, being careful to have

the standard strip superimposed closely upon the exposed

paper with the long dimension of the two papers in the same

direction. Make the comparison in the light from a daylight

fluorescent lamp, or equivalent source, with illumination

of 50 foot candles or more on the papers. The plane of the

incident and reflected rays should be perpendicular to the

long edge (machine direction) of the paper and booklet. The

incident light should strike the paper at an angle of 45°,

and the angle of viewing should be perpendicular to the

surface of the paper. Avoid touching the surfaces of the

exposed paper and the standard strips with the fingers, as

the paper is sensitive to moisture and is easily soiled.

From the comparison, estimate the exposure (to the

nearest Standard Fading Hour) that would duplicate the

fading of the test piece. For example, if the color of

the test piece was considered to be mid-way between those

of the standard strips labelled 16 and 20 SFH in the

booklet, the estimated value would be 18 SFH. If the test

piece had been exposed for 20 hours, the severity factor

SFH/CH would then be 18/20 = 0.9, the value recommended for

normal operation of a carbon arc. The exposure in SFH at

other times would then be taken as 0.9 of the time in

clock hours

.

The severity factor for the carbon arc should normally

be kept between 0.8 and 1.0 at 20 CH. If it is found to be

10
outside this range, change of the transformer tap or other

adjustments should be made until this condition is attained.

In making preliminary comparisons of faded papers and

standard faded strips, it is permissible to breathe on the

paper momentarily to increase its moisture content. Final

comparisons, however, should be made after the paper has

been conditioned overnight or longer in the dark in air at

50% relative humidity at room temperature.

7.2 REFLECTANCE MEASUREMENTS

Although the paper and booklets were originally

designed for simple visual estimation of the fading of test

strips without the use of any accessories other than the

eye, greater precision can be obtained by the use of an

instrument measuring a property which changes with exposure.

The property used at the National Bureau of Standards in

evaluating the standard faded strips in the booklets is the

45°, 0° luminous-directional reflectance factor R, as measured _d

with a green filter with a Hunter Color and Color Difference

Meter (Gardner type) [5] . This is equal to the tristimulus

value Y. As with the visual estimation, the plane of the

incident and reflected rays should be perpendicular to the

long edge of the paper. Likewise the incident light should

strike the paper at an angle of 45°, as the reflectance

normal to the surface is measured. The individual numerical

value found at the time of preparation of each strip in the

booklet is written in ink on the strip itself. The corresponding exposure (to the nearest 0.1 SFH) may be obtained

from this value by interpolation in the table or graph

furnished with the Certificate of Calibration for the

particular lot of paper. In this manner the exposure of

the standard faded strips can be fixed much more accurately.

Their position in the booklet indicates the exposure only

to the nearest unit SFH.

11
The papers may change in reflectance on further exposure

to light, heat, humidity or by mishandling or soiling.

Reflectance measurements on different instruments often

show appreciable differences, even when measuring the

same piece of exposed paper. Differences in reflectance

readings can arise from differences in geometry of incident

and viewing light beams, linearity of photometric scales,

spectral sensitivity of the photocell, spectral transmi ttance of filters, and similar causes.

Reflectance measurements are made with the paper

against a black background with the machine direction of

the paper perpendicular to the plane of the incident and

reflected rays. The machine direction (grain) of the paper

lies along the longer side of both the unexposed paper and

the standard strips in the booklet.

Most ref lectometers yielding tristimulus Y values can

be adjusted, if necessary, to make their readings agree with

those shown in ink on the standard faded strips. For repeated standardizations a porcelain plaque of about the same,

spectral reflectance as the exposed paper is recommended

in order to avoid repeated handling of the paper.

Some ref lectometers have a measurement precision that

permits readings to four significant figures , as shown in

the graph and table contained in the Certificate of

Calibration. However, a comparison of reflectance measurements, on single strips given the same exposure shows a

standard deviation of about 0.00 2. This corresponds to about

0.8 SFH near 20 SFH and about 0.7 SFH near 6 SFH.

If the user has available an instrument measuring

reflectance and if the values observed with the six

standard faded strips agree with or can be adjusted to agree

with the values of Y written in ink on each strip , the

instrument is in agreement with the one at the National

Bureau of Standards. Consequently the graph and table

12
given in the Certificate of Calibration can be utilized to

obtain SFH for any test strip exposures.

7.3 CALIBRATION BY OTHER PROPERTIES

If the agreement just mentioned can not be obtained,

or if the available instrument measures some property of

the paper other than the tristimulus value Y, the standard

faded strips may still be used to calibrate this instrument.

The property, presumably an optical property, can be any

one which changes quantitatively with exposure. In this

case a measurement is made on each of the six standard

faded strips. The values found with the user's instrument

are plotted as a function of the exposure of the standard

strips in SFH (obtained from the reflectance marked on

each strip) to obtain a six-point calibration curve for

the property measured. When the user's instrument is

calibrated in this manner, the same number of SFH should

be obtained from a newly-exposed test strip of paper as would

have been obtained if the calibration had been made in

terms of any other property, including specifically the

tristimulus Y value used at the National Bureau of Standards.

8. FREQUENCY OF CALIBRATION

Many laboratories always expose one or more strips of

paper along with the textile specimens under test, thus

obtaining a calibration every time the arc is operated.

This is desirable since the fading rate of a carbon arc

lamp may change from day to day or even during a test.

If the paper is not used during every run, a definite

schedule for calibration at fixed intervals, should be

developed by each user in accordance with his own

requirements. Certainly the arc should be recalibrated

whenever a new lot of carbons is put into use or any other

13
significant change is made. The more frequently checks are

made, the greater will be the assurance that the lamp is

performing as desired.

For obtaining exposures near to a desired number of

SFH, duplicate strips of paper may be used, so that a

preliminary value of the severity factor may be obtained

from one strip before the estimated end of the run. The

following instructions illustrate the procedure for

obtaining an exposure of 20 SFH

.

Place the textile specimen and two (or more if desired)

pieces of the paper in the lamp at the same time, side by

side. Remove one of the papers from the lamp about 4 hours

before the estimated end of the test, noting the time.

Allow this paper to stand in the dark at room temperature

for 2 hours; compare the fading with that of the standard

faded strips; and obtain the severity factor for converting

clock hours to SFH as already outlined. Use this factor

to calculate the time in clock hours to give the desired

number of SFH at the end of the test.

The piece of paper left in the lamp with the textile

will have received the same radiant-energy exposure as the

textile at the end of the test. The actual exposure in

SFH at the end of the test will then be obtained by rating

the fading of this paper with the standard faded strips in

the booklet. The result can be used as evidence that the

test was as desired or sufficiently near to it, or that the

test must be repeated.

For long exposures, a succession of papers will have

to be used and the number of Standard Fading Hours shown

by them added together to obtain the total exposure. In

making such tests, the paper should be changed with each

change of carbons

.

14
9. PROCEDURE FOR ORDERING PAPER AND BOOKLETS

Different issues of the light-sensitive paper have

different fading rates. Consequently, the booklets of

standard faded strips and the fading curve supplied in the

Certificate of Calibration for any one issue of unexposed

paper apply to that issue only; therefore booklets and

unexposed paper of the same issue should be used together.

The lower case letter at the end of the standard sample

number indicates the issue of the standard sample. The

booklet of standard fading strips No. 701c should be used

with unexposed paper No. 700c. It cannot be used with

No. 700b or any earlier issue of the paper. However, when

the supply of unexposed paper No. 700c at NBS becomes

exhausted, a new issue will be supplied as Standard Reference

Material 700d. It will then become necessary for the

customer to order a new booklet of standard faded strips

No. 701d to be used with the new issue of paper. This is

unavoidable because it is not possible at present to control

the manufacture of the paper so that all of the issues of

paper are exactly the same with regard to fading rate.

The unexposed paper cannot be used satisfactorily

without the booklet of standard faded strips because of

differences in measuring instruments, as outlined earlier.

This publication, explaining the use of the paper and

booklet, and a Certificate of Calibration accompany each

shipment of a sample of the unexposed paper or booklet of

standard faded strips. They will be sent separately, free,

on request.

Order by Standard Reference Material Number (e.g., 700c

for the unexposed paper; 701c for the booklet of standard

faded strips). Address orders to:

15
Office of Standard Reference Materials

National Bureau of Standards

Washington, D. C. 20234

Attention: Standard Reference Materials Unit

Prices and terms of purchase are given in NBS Miscellaneous

Publication 260, "Catalog and Price List of Standard

Reference Materials Issued by the National Bureau of

Standards "

.

16
10 . REFERENCES

1] Wood, L. A . , Shouse, P. J., and Passaglia, E., "How just

appreciable fading of AATCC L-4 wool standard is related

to exposure time", Textile Chemist and Colorist 2_,

No. 11, 28/182 (1970)

.

[2] Launer, H. F., "Light-sensitive papers as controls for

testing textile colorf astness and stability of

materials under arc- lamp exposure", J. Res. Nat. Bur.

Stand. 41, 169 (1948)

.

1 3 J Boor, L. and Trucker, S. L., "An improved Fade-Ometer "

,

ASTM Bulletin No. 189, p. 38, April 1953.

[4] Wood, Lawrence A., "The use of dew-point temperature in

humidity calculations", J. Res. Nat. Bur. Stand. 74C , 117 (1970).

[5] Hunter, Richard S., "Photoelectric color-difference

meter", J. Optical Soc. Am. 48, 985 (1958).

17
form NBS-114A (1-711 U.S. DEPT. of comm. 1. PUBLICATION OR REPORT NO. 2. Gov't Accession

oDiDLiuuKArniL ID 1 irtrD A DUlr piATA ua i a \Tnn n-n- r r\ a n No. InBS SP 26 0 — 4X

SHEET

3. Recipient's Accession No.

4. title and subtitle standard Reference Materials:

Use of Standard Light-Sensitive Paper for Calibrating Carbon Arcs Used in Testing Textiles for

Cclorf astness to Light

5. Publication Date August 1972

6. Performing Organization Code

7. AUTHOR(S)

Lawrence A. Wood and Paul J. Shouse

8. Performing Organization

9. PERFORMING ORGANIZATION NAME AND ADDRESS NATIONAL BUREAU OF STANDARDS DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Address Same as No. 9.

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.) The use of NBS Light-Sensitive Paper and NBS Booklets of Standard

Faded Strips in the standardization of carbon arcs is described.

These lamps are used to determine the fading characteristics and

degradation of textiles and other materials when subjected to

visible and ultraviolet radiation. The light-sensitive paper

is useful in calibrating the arcs in terms of NBS Standard

Fading Hours CSFH) or equivalent exposure in the NBS Master

Carbon-Arc Lamp

.

17. KEY WORDS (Alphabetical order, separated by semicolons) _ , , , . . . Carbon-arcs, standardization of;

color-fastness, testing of; fading tests, standardization; light-sensitive

aper

,

—light-sensitive

—textiles ,—f adi

p8^SvAiLAB

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UNCLASSIFIED

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2k

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