NATIONAL BUREAU OF STANDARDS REPORT

9845

JUST APPRECIABLE FADING OF THE AATCC

L-4 WOOL STANDARD AND THE NBS STANDARD

FADING HOUR (SFH)

For

American Association of Textile Chemists and Colorists

Committee R A — 50 On

Colorfastness to Light

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

3111734 May 24, 1968 9845

JUST APPRECIABLE FADING OF THE AATCC

L-4 WOOL STANDARD AND THE NBS STANDARD

FADING HOUR ((SFH)

by

Lawrence A. Wood, Paul J. Shouse, and Elio Passaglia

to American Association of Textile Chemists and Colorists

Committee R A — 50 On

Colorfastness to Light

IMPORTANT NOTICE NATIONAL BUREAU OF ! for use within the Governmen

and review. For this reason, whole or in part, is not autl Bureau of Standards, Washin

the Report has been specitica

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015

;ress accounting documents intended

is subjected to additional evaluation

ire listing of this Report, either in the Office of the Director, National by the Government agency for which

I copies for its own use. <NBS>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

3111734 May 24 , 1968 9845

JUST APPRECIABLE FADING OF IKE AATCC

L-4 WOOL STANDARD AED THE NBS STANDARD

FADING HOUR (SFH)

by

Lawrence A. Wood, Paul J. Shouse, and Elio Passaglia

to

American Association of Textile Chemists and Colorists

Committee RA-50 On

Colorfastness to Light

JTJST APPRECIABLE FADING OF THE AATCC

L-4 WOOL STANDARD AND THE NBS STANDARD

FADING HOUR (SIU)

Page

1. Wool Standards 1

2. Light Sensitive Paper 3

3. Standard Fading Hours (SFH) 4

4. Exposure of Wool Specimens 9

5. Visual Ratings 10

6. Spectrophotometric Measurements l4

7. Color Differences 16

8. Conclusions py

8.1 Visual Ratings py

8.2 Spectrophotometric Measurements p8

9 . Summary 21

Acknowledgment 23

References 24

Appendix 26

Color Difference Equations 26

Color Difference References 3 P

SUMMARY OF CONCLUSIONS

The color difference resulting from just appreciable fading of

the wool standards (as judged by the panel) can be expressed as about

3 NBS units. Equivalent values in other systems are about 1.5 for

either the Scofield-Hunter relation or the Glasser-McKinney-Reilly -

Schnelle cube-root relation, as compared with about 4.5 MacAdam units

when use is made of the Friele -MacAdam - Chickering-Billmeyer

treatment.

Just appreciable fading of the wool standards was produced by an

exposure of slightly less than l4 clock hours in the NBS Master

carbon-arc lamp.

The exposure resulting in just appreciable fading of the wool

standards is equivalent to about 11 NBS Standard Fading Hours.

The first two conclusions are independent of each other and are

not dependent in any way on the use of the NBS Light Sensitive Paper

for calibration of the arc. The third, conclusion is based on the use

of the paper; this showed that the lamp was operating normally with

a severity factor F near 0.9, as recommended.

1. Wool Standards

Carbon arc lamps are widely used in the textile and other

industries 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 undergoing measurable

changes when exposed to this radiation, [l]

The first set of textile standards recommended by the American

Association of Textile Chemists and Colorists was described in their

1931 yearbook, [l, 2] Other standards were recommended in later

years until 19^2 , when there were 8 blue standards designated

LD 1 through LD 8. [ 3 ]

"LD 4 after 10 hours exposure should show barely perceptible

fading--after 20 hours^ marked fading. However, the terms perceptible

and marked are loose and it has been proved that every operator has

his own different conception of these terms". [ 3 ]

These early standards, like the blue wool standards sponsored

by the International Organization for Standardization [ I. S.O./TC38/

SCI USA Section 93 > 310, page 55 February 1965] and still currently

in use in Europe, used a different dye for each of the 8 standards.

1
The current set of 8 blue wool AATCC standards was developed by

Christison in 1944 [4] and issued in 1945 C 5 ] • Unlike the previous

standards these are prepared by blending wool fibers. As described

in the AATCC Technical Manual [6]

:

"These standards are specially

prepared by blending varying proportions of wool dyed with a very

fugitive dyestuff, Erio Chrome Azurole B (C. I. 43830), and wool dyed

with a fast dyestuff, Indigosol Blue AGG (C. I. 73801), so that each

higher numbered standard is approximately twice as fast as the

preceding standard”.

Seibert in 1947 [2] makes the following statement:

"Standards 2 to 8 serve to grade colors that fade to an

appreciable degree on exposure in the Fadeometer for between 2.5 and

5 hours; 5 and 10 hours; 10 and 20 hours; 20 and 40 hours; 40 and

80 hours; 80 and 160 hours; and No. 8, the fastest, between 160 and

320 hours".

Thus Standard L-4 is intended for use in the range between

10 and 20 hours.

The term "just appreciable fading" is now defined by the

AATCC [6] as follows:

"3*1 'Just appreciable fading 8 in the following methods means

a change in color of any kind (whether a change in hue or saturation,

or becoming lighter or darker) which is immediately noticeable in

comparing the exposed area of the specimen with an unexposed area, when

viewed in north sky light or equivalent source with illumination of

50 foot-candles or more on the surface. If closer inspection or a change of angle is required to make certain that there is a change in

color, the fading is not considered to be ’appreciable 8 . 2
"3.2 "Just appreciable fading* is also the degree of contrast

between the pair of pieces of paper illustrating step 4 of the

International Geometric Gray Scale for Evaluating Change in Color."

No agreement has been reached on proposals to define just

appreciable fading of the wool standards in terms of any quantity

that can be measured directly with an instrument.

The unit of time in 1944 was called a "Fade-Ometer Hour", but

the conditions of operation and the characteristics of the arc were

not sufficiently well-defined to make this a very satisfactory unit.

Surveys [3,7] of the arcs in use at about this time showed variations

by a factor of two or three .in the time required by different arcs to

produce the same degree of fading.

2. Light-Sensitive Paper

Research work at the National Bureau of Standards over a period

of years beginning about 1940 led to the development of light-sensitive

paper strips as reference materials for the control of the dosage of

radiation from carbon arcs. [8] Successive lots of these papers have

been issued since 1945* C 9 D The luminous reflectance R^ (equal to

the tristimulus value Y) as measured with a. Hunter Color and Color

Difference Meter (Gardner type) [10] is the quantity now used in the

calibration of the light-sensitive paper.

3
3. Standard Fading Hours (SFH)

Over the years, the conditions of operation of the master arc

lamp used -with the papers have been controlled and specified with

progressively increasing detail.

The records available to the present authors do not make it

entirely clear just how the unit standard fading hour used at the

National Bureau of Standards was established. There is some evidence

that in 19^7 a change in the controls was made reducing the intensity

of the radiation by 10$. [11]

Three quotations are pertinent:

1. "As a temporary working basis 20 Standard Arc Hours has

been defined as corresponding to ’appreciable fading’ of AATCC No. 7

Blue Wool Standard." (NBS Directions for use of Light-Sensitive

Paper July 1, 1947)®

2. "The setting adopted was based on the ’Fade-Ometer Hour'

used for some years in industry for rating colorfastness of textiles

and dyes." (NBS General Letter dated July 1947; NBS Letter

Circular LC 906, May 21, 1948).

3. "The Standard Fading Hour scale now under trial was selected

with the advice and cooperation of the committees on color fastness

of light of the American Association of Textile Chemists and Colorists

and of the American Society for Testing Materials. Samples of the

paper were exposed simultaneously with samples of the AATCC dyed wool

lightfastness standards. When the latter had faded to an extent the

committees considered representative of 20 Fade-Ometer hours of

exposure the paper was considered to have faded to an extent representative of 20 Standard Fading Hours of exposure. "(NBS Circular

LC 934 January 13,1949) 4
4. "Twenty standard fading hours of exposure in the master lamp

is equivalent in fading action to 20 clock hours of exposure in the

well known Atlas Electric Device Company's FDA-R Fade-Ometer, based

upon the average results of tests in 130 of these lamps." (NBS

Letter Circular LC 1004 August 30 > 1951 ).

It is presumed that the tests referred to were those reported

by Seibert in 1945* [7]

These four descriptive definitions, which were repeated in later

publications, may or may not have been consistent with each other.

We know of no numerical values which would serve as a basis for

present-day comparisons. Consequently we consider it impossible to

determine at the present time whether these four definitions were

consistent with each other and, if not, which of them was actually

given the greatest weight in controlling the arc. Indeed the answer

to this question is not considered of very great importance at present,

since we have no information concerning the early control of several

factors now known to be of importance. Among the most significant

of these axe temperature, humidity, and air flow.

In any event, since February 25 , 19^9 (see KBS Letter Circular

LC 1004 August 30, 195l) every effort has been to keep constant

the dosage of radiation represented by 1 Standard Fading Hour

(SFH) at the National Bureau of Standards.

5
With this purpose, over the years repeated observations have

been made of the color changes found in a given lot of paper for a

given number of hours of operation of the lamp. No significant

differences have been found in measurements made in our own

laboratories. Each new lot of paper has been compared carefully

with one or more of the preceding lots a.t the time it has been

introduced. The exposures of the new lot have then been expressed

in terms of the SFH defined by the previous lots.

When a major change in the lamp was made in 1954 by the

installation of an enclosed arc in place of an open arc, the output

was carefully compared with that of the earlier lamp by the use of

the light-sensitive paper, and ratings with the new lamp were

continued in terms of the SFH already in use.

The present NBS Master Lamp is an Atlas Electric Devices

SMC-R Fade-Ometer with a drum diameter of 20 inches (50.8 cm) rotating

at 3 revolutions per min., using No. 70 Solid Carbons and No. 20

Cored Carbons. The black-panel temperature is held at 150±5°F

( 65.6 ± 2°C) by the use of 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 so adjusted as to maintain the black panel temperature at 150°F. The

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

temperature (77°Fj 25°C) and humidity (45$>»Dew Point 54. 5F, 12.5°C),

and size of our present laboratory are such that under these

conditions the temperature of the exit air is usually 117 ± 2°F

( 47.2 ± 1°C).

6
Moisture is added to the circulating air by -water sprayed from a

rotating disk so as to raise the relative humidity of the exit air to

30°lo at the dry bulb temperature of 117°F. A bimetallic thermostat

responding to wet-bulb temperature starts and stops the rotating

disk. In this manner the humidity is controlled by aut omat i c ally

maintaining the wet bulb temperature at the desired value of 87°F

(30.6°c) in the present instance.

The dew-point under these conditions is 80°F (26.7°C). It would

not be at all convenient to maintain a higher humidity than this,

since a dew-point higher than room temperature gives rise to

condensation difficulties when the air is allowed to cool from

117 °F to room temperature.

Under these conditions, with an arc voltage of 120-145 v. A. C.

and an arc current of 15-17 amp (ranges specified by the manufacturer)

,

20 hours of operation of the lamp are found to fade the lightsensitive paper to an extent equivalent to about 18 SFH.

Defining a severity factor F for a given run as the ratio of

standard fading hours (SFH) to clock hours (CH), one finds that F

is thus about 0.9, as recommended [12, 13 ]

7
The severity F is obviously lower than that employed some years

ago (when F=1.0). This reduction is probably due chiefly to the

lowering of the effective black panel temperature from about

l65 °F (73*9°C) to 150°F. The present authors have been unable to

discover from a study of the available publications any logical

reason for the difference between the black-panel temperature of

150 0 ± 5°F maintained in the NBS Master Lamp ever since the time

that the black panel was first introduced, and the corresponding

figure of 145° ± 5°F recommended in the AATGC Method 16 a - 1964. It

is hoped that this annoying discrepancy can be eliminated in the

future

.

It is possible to vary the severity factor somewhat by varying

the arc voltage by using a different transformer tap. Only a limited

range of adjustment is possible by this means. The severity factor

is altered markedly by deviations from the standard conditions of

temperature and humidity.

The objectives of the work described here were: (1) to make a

study of the visual ratings of samples of the 1957 L-4 Wool Standard

which had received known dosages of radiation in the present NBS

Master Lamp, and ( 2 ) to determine the relation between spectrophotometric color difference and dosage for these specimens.

8
4. Exposure of Wool Specimens

Sixty specimens of the 1957 lot of AATCC L-4 Standard Wool

[2,6] 2 3/4 x 4 3/4 in. (6.98 x 12.1 cm) -were cut from pieces

18 x 28 in. (45.7 x 71*1 era) furnished by the Technical Director

of the AATCC [l4]. An area about 5»0 x 4.0 cm. at one end of the

specimen was exposed (without backing) in October 1966 in the KBS

Master carbon arc lamp.

Ten specimens were faded at a time simultaneously with 9

specimens of the KBS Light-Sensitive Paper Lot 700a. [15] Six

different exposures, namely 10.1, 12.0, 14.0, 16.0, 18.0, and 20.0

hours were made. The luminous reflectance of the faded paper

strips was measured with the Hunter Color and Color Difference

Meter [ 10 ] as described in KBS Letter Circular LC IO36. [IS] The

numbers of SFH corresponding to each value of reflectance read from

the graph given in LC 1036 were as follows: 7«2, 9 »lj 11.6, 13*6,

15.0, and 17»7 SFH. Therefore the values of the severity factor

F, the ratio of SFH to clock hours, were found to be 0.71> O.76,

O.83, O.85, and O.89 respectively, in approximate agreement with the

recommendation [12,13] that the arc be adjusted to give an F ratio

near 0.9.

9
5 . Visual Rating of Wool Specimens

The judgment of "just appreciable fading" was conducted

independently by a panel of 6 trained observers selected by

Mr. F. A. Sievenpiper of Allied Chemical Co. at the request of the

AATCC Committee RA50 (Committee on Colorfastness to Light). They

were

:

1. Leander Ricard, Chairman, Committee RA50

I. C. I. Organics Inc. Providence R. I.

2. Otto A. Ofjord, Secretary, Committee RA50

E. I. DuPont de Nemours and Co., Wilmington, Delaware

3. Edward W. Boland

American Aniline Products, Lock Haven, Pennsylvania

4. Louis J. Provenza

Geigy Chemical Co., Yonkers, N. Y.

5. Lewis Oechslin

American Viscose Co. Marcus Hook, Pennsylvania

6. George Keilman

Allied Chemical Co., Bala Cynwyd, Pennsylvania

10
The panel assembled at the National Bureau of Standards, on

February lL, 1967 * Each panel member was given a set of 10 specimens

randomly picked from the 6 different exposures and asked to make an

independent judgment without consultation by placing each of them

in one of 3 categories:

(1) Less than just appreciably faded (Score, -l)

(2) Just appreciably faded (Score, 0)

( 3 ) More than just appreciably faded (Score, +l)

In making his selections each observer held the specimens in

a Macbeth Illuminator set to furnish an illumination equivalent to

north sky light of 200-225 foot-candles. Comparisons could be made

as often as desired with Step 4 of the AATCC International Gray

Scale for Evaluating Change in Color. [6] In the second round each

observer had a different set of 10 specimens. This was continued

until all 6 observers had independently and individually rated all

60 specimens, giving 360 ratings in all.

The effect of variation from specimen to specimen is considered

first. The sum of the scores assigned by the 6 observers to a given

specimen was taken as the score of that specimen. For example, if all

6 observers rated a specimen more than just appreciably faded it would

receive a score of +6. The total of the 10 individual specimen scores

was divided by 10 to give an average specimen score for each exposure.

In Fig. 1 the circles represent the average specimen score as a

function of the exposure in SFH.

11
The crosses in Fig. 1 represent the frequency distribution

of the individual specimen scores. The specimen numbers (indicated

at the right of each cross) represent position around the drum

during the exposure. The frequency of each score (i. e. the number

of specimens having a given individual specimen score) is plotted

along the axis previously used for SFH, with values increasing to the

right and measured from a zero axis placed on the vertical line

through the circle in each case. The vertical axis itself is scaled

to represent the average or individual specimen score, as the case

may be.

No significant pattern showing the effect of specimen position

during exposure is discerned here. The spread of scores is quite

wide in the 4 intermediate exposures but becomes appreciably narrower

at the two extremes, where judgment would be expected to be easier.

Only one specimen (No. 19) of the 10 in the lowest exposure group was

judged to be less than just appreciably faded by all observers

(score -6.0); and only one specimen (No. l4) of the highest exposure

group was judged to be more than just appreciably faded by all

observers (score, +6.0). There were 2 such specimens at each of the

adjacent exposures. Of all the 60 specimens investigated there was no

single specimen which was rated as just appreciably faded by all 6

observers. In the three instances where the individual, specimen

score was 0, positive scores were balanced by negative.

12
The graph drawn through the circles representing the mean

specimen score at each exposure would he expected to he asymptotic

to the value -6 at the lowest values of exposure and to +6 at the

highest, since there were 6 observers. This appears to he

approximately true, the actual scores attained at the lowest exposure

being about -4, and at the highest, about +4. This means that only

about two-thirds of the specimens given the lowest dosage were rated

as under-exposed by the average observer and that only about twothirds of the specimens given the highest dosage were rated as overexposed. The remaining one-third in each case (with a single

exception) were rated as just appreciably faded.

The graph drawn through the circles representing mean scores

passes through 0 at about 11 SFH. Under the present conditions then,

11 SFH is seen to give rise to just appreciable fading of the L-4

Wool Standard, as judged visually by the 6 observers.

The effect of variation from observer to observer is shown in

Fig. 2. The sum of the scores assigned by a given observer to the

10 specimens of a given exposure was taken as the individual observer

score. Thus for example if an observer rated all 10 specimens more

than just appreciably faded he would receive a score of +10 for that

exposure. The total of all the individual observer scores was

divided by 6 to give an average observer score for each exposure.

In Fig. 2 the circles represent the average observer score as a

function of the exposure in SFH.

13
As -would, be expected this quantity is found to be somewhat

larger in absolute value than the average specimen score plotted in

Fig. 1. This should show an asymptotic approach to the value -10

at low exposures and +10 at high. The graph drawn through these

points , like that of Fig. 1, passes through 0 at about 11 SFH.

Here the frequency curves are analogous to these in Fig. 1,

and show the number of observers reporting a given individual

observer score. The identifying number arbitrarily assigned to each

observer is shown near each respective point. It is not related

to the order in which the observers are listed at the beginning of

this section. It is immediately apparent that there is a very

significant pattern showing differences among observers. Observers

Numbers 3 and 4 assigned consistently high scores, while Observers

5 and 6 were consistently low.

6. Spectrophotometric Measurements of L-4 Wool Specimens

The spectral directional reflectance of the 60 specimens was measured by personnel of the NBS Colorimetry and Spectrophotometry

Section. The instrument used was a General Electric recording

spectrophotometer [ 16 ] equipped with slits of approximately 10 nm of

spectral width over the visible spectral region for the condition of

included specular component. Corrections were made for zero-curve

errors and for the NBS Vitrolite standard. Observations were made

on the exposed and unexposed portions of each specimen and repeated

after a 90° rotationof the specimen. The spectral reflectance was measured at each of 36 wave lengths from 400 to 750 nm, for a total

of 8,640 observations. CIE source C was used for illumination.

14
Each observation was recorded automatically on punched paper

tape by digital readout equipment. The values were transferred from

the tape to punched cards for processing by a high speed digital

computer. Computer programs were written to yield chromaticity

coordinates x and y and daylight reflectance Y. Additional

computer programs were then written to obtain color differences between

the exposed and unexposed portions of each of the 60 specimens.

Definitions and descriptive references [A1-A15] for various

color difference units have been treated in the Appendix.

Typical observations of spectral reflectance for a single

specimen are plotted as a function of wave length in Fig. 3» For

comparison the corresponding reflectances for light-sensitive paper

700a are shown. The change in spectral reflectance of the paper

during exposure is from 10 to 20 times that noted for the wool.

15
7. Color Differences

The computer program furnished, the color difference in MBS units

between the exposed and unexposed portions of each of the 60 wool

specimens. The relations used are given in Part I of the

Appendix [A2-A5]. Table 1 lists AE^ the arithmetic mean of the

10 color differences calculated for the 10 specimens for each

exposure, together with A(Sp Ref . )gyQ,uhe average change in spectral

reflectance at 670 run (in the region of greatest change of spectral

reflectance) and AY the average change in tri-stimulus value. The

numbers in parentheses indicate the coefficient of variation (ratio of

standard deviation to mean value) of a single observation from the

arithmetic mean of the 10 observations at each exposure. The table

also lists the standard deviation and coefficient of variation of a

single ratio from the mean of the 6 ratios reported.

Four different relations described in the Appendix were used to

obtain the color differences shown in Table 2« The computer program

furnished the 10 individual values for AE^ at each of the 6 exposures.

The value AE^ shown in the table is the arithmetic mean of these 10

values. On the other hand, the labor involved in making 60

computations of AE0 AE^, waY

’was no^ considered to

be justified. Consequently the average values of X, Y, and Z for each

exposure were taken and a single computation was made from these

average values to obtain the results shown in the table. This method,

of course, yielded no information about the standard deviation of

a single observation.

16
8. Conclusions

8.1 Visual Ratings

The observers were asked to place the specimens in three

categories, but were given no instruction regarding the range which

might be covered by the middle category ("just appreciably faded").

Of the 360 ratings, there were 99 in Category 1, 127 in Category 2,

and 134 in Category 3» Thus it appears that there was a tendency for

the observer to assign about the same number of specimens to each

category and to maJbe the range of just appreciable fading about as

wide as those of the underexposed and overexposed specimens furnished

in the present study.

Of the specimens exposed for the shortest time (7*2 SFH) only

about two-thirds were rated as less than just appreciably faded by

the average observer. Of the specimens exposed for the longest

time (17.7SFH) only about two-thirds were rated as more than just

appreciably faded by the average observer. The remaining one-third

in each case (with a single exception) were rated as just

appreciably faded.

The graph representing mean specimen scores (Fig. l) and the

graph representing mean observer scores (Fig. 2) both pass through

zero at about 11 SFH. This means that 11 SFH as measured under the

presently-specified conditions of operation of the Master Arc Lamp

at the National Bureau of Standards gives rise to just appreciable

fading of the L-4 Wool Standard, as judged visually by the 6 panel

members. The position of the specimen around the drum during

exposure was found to have no significant effect. None was to be

expected since the drum was rotated constantly about an axis

intended to pass through the arc. 17
Two of the panel members were found, to have given consistently

high scores, while two gave consistently low scores, as compared with

the average scores or with those of the other two. From the ratings

of the first pair alone one would have concluded that just

appreciable fading occurred at about 10 SFH; from the ratings of

the second pair alone, the value would have been 13-14 SFH.

Of all 60 specimens investigated, there was no single specimen

which was rated as just appreciably faded by all 6 panel members.

Conclusions drawn from visual observations on single specimens

are thus of doubtful significance.

8.2 Spectrophotometric Measurements

Measurements of spectral reflectance over the visible

range of wavelengths by the General Electric Recording Spectrophotometer showed wide variations from specimen to specimen. Color

differences computed for the fading of each specimen also showed

large variations. The standard deviation of a single value of color

difference from the mean was found to lie in the range 0.35 to 0.50

WBS unit of color difference# This corresponds to a coefficient of

variation of about 20$ at the shortest exposure. This coefficient

is about 15$ at the intermediate exposures and about 10$ at the

longest. The values calculated are shown in Table 1. With only one

exception the coefficient of variation of the color difference values

is less than that of either the change in spectral reflectance at

670 nrn or that of the change in tri- stimulus value Y.

18
It can be seen from the columns of ratios that the change in

spectral reflectance and the change in tri-stimulus value are each

approximately a fixed multiple of AE^, the color difference in

KBS units.

It "will be noted from the columns of ratios in Table 2 that

the values in two instances are about 0.5^ and in the other about

1*5 times the values expressed in KBS units. These ratios are seen

to show no systematic trend with varying times of exposure. Thus,

apart from considerations of precision, there appears to be no

particular advantage in using one relation rather than another as

a quantitative measure of the limited type of color differences

produced by the fading of the L-^+ Wool Standards. The coefficient

of variation of the ratios for AE^ appear to be somewhat smaller than

that for the AE^ and AE^ ratios. This would indicate that AE^

shows a better correlation with AE^ than the others.

19
It was noted that the average color difference AE^ was roughly

proportional to the square root of the time of exposure, t. The

method of least squares was applied to the 7 observations including

a value of AE-j = 0 for t = 0 as well as the 6 different exposures.

When the color difference was in MBS units and the time in SFH the

empirical relation found was:

ZE = 0.909 t

1/

2

where the coefficient O .909 had a standard deviation of 0.030 or

3 - 3$.

Table 3 shows the color difference AE^ as calculated from the

equation at several different times of exposure. It also shows the

other quantities used in Tables 1 and 2, as calculated from AE^

by the use of the respective ratios. The exposure marked with an

asterisk (ll SFH) is that rated by the panel as producing Just

Appreciable Fading.

The observed values of AE^ are plotted in Fig. k against the

exposure time and also against the square root of the exposure time.

The curve and the straight line are those representing the empirical

equation from the least squares analysis.

20
Three points shown as triangles in Fig. 4 represent observations

on 4 specimens at each of 3 exposures of L-4 Wool Standards measured

in our laboratories in 1966 as a preliminary to the present

investigation. The agreement with the present results is quite

satisfactory.

From the equation it may be calculated that the standard

deviation of a single value of color difference , which has been given

as ranging between 0.35 and 0.50 MBS unit, corresponds to a

standard deviation of exposure time of 2.6 to 3«^ SFH. Nearly the

same values of standard deviation were obtained for the k specimens

at each of the 3 exposures studied in 1966 .

The conclusion is that the precision of measurement is such that

only two-thirds of a group of single measurements of color difference

of the L-4 Wool Standards would be expected to fall within a range

of ± 3 SFH around the mean value.

9 . Summary

Finally we recapitulate the three major conclusions which

may be drawn from the present investigation:

21
1.

The color difference resulting from just appreciable fading of

the -wool standards (as judged by the panel) can be expressed as about

3 NBS units [A2-A5]. Equivalent values in other systems are about

1.5 for either the Scofield-Hunter relation [A2-A9] or the GlasserMcKinney -Reilly Schnelle cube-root relation [Ah^AlO] as compared

with about 4.5 MacAdam units -when use is made of the Friele -MacAdam -

Chickering- Billmeyer treatment [AUL-A15].

2. Just appreciable fading of the -wool standards -was produced

by an exposure of slightly less than l4 clock hours in the MBS Master

carbon-arc lamp.

3. The exposure resulting in just appreciable fading of the

wool standards is equivalent to about 11 MBS Standard Fading Hours.

The first two conclusions are independent of each other and are

not dependent in any "way on the use of the MBS Light Sensitive Paper

for calibration of the arc. The third conclusion is based on the use

of the paper; thig showed that the lamp was operating normally with

a severity factor F near 0.9> as recommended.

22
ACKNOWLEDGMENT

The authors are grateful to John Mandel of the MBS Institute for

Materials Research for suggesting the statistical design of the

visual ratings and for discussions of the statistical analysis of

the results , and to I. Nimeroff and John C. Schleter of the MBS

Colorimetry and Spectrophotometry Section for arranging for the

spectrophotometric measurements and for discussions of color

differences. We should also like to thank Mr. Frank Rizzo and

Lt. Ronald Cronise of the U. S. Army Watick Laboratories for recent

references and information concerning color difference equations.

23

REFERENCES

[1] W. H. Cady, The historical background of the new standards for

lightfastness, American Dyestuff Reporter 33., 29 (1944).

[2] C. A. Seibert, Report of Committee on Lightfastness^ American

Dyestuff Reporter 36 , 201 (1947).

[3] P. J. Wood, Calibration of Fadeometers, American Dyestuff

Reporter 31, 595 (1942).

[4] Hugh Christison, New proposed standards for lightfastness,

American Dyestuff Reporter 3_3, 33 (1944) •

[5] American Association of Textile Chemists and Colorists

Light fastness Standards, American Dyestuff Reporter 36, 194

( 1947 ).

[ 6 ] American Association of Textile Chemists and Colorists

Technical Manual B-71 Colorfastness to light: General Method

Method I6 -I96LT.

[ 7 ] C. A. Seibert, A proposed method for the calibration of carbon

arc lamps used for testing and grading lightfastness,

American Dyestuff Reporter 34, 272 (1945).

[ 8 ] Herbert F. Launer, Light-sensitive papers as controls for

testing textile colorfastness and stability of materials under

arc lamp exposure, J. Research Natl. Bur. of Standards 4-1 ,

169 (1948) RP 1916 .

24
[9] Herbert F. Lamer, The standard fading lamp at the National

Bureau of Standards and means of calibrating other lamps in

terms of it, American Dyestuff Reporter 3j4, 264 (1945).

[10] Richard S. Hunter, Photoelectric color difference meter,

J. Optical Soc. of America 48, 9^5 (1958).

[11] William A. Holst, Report of Subcommittee on Fastness to Light,

American Dyestuff Reporter 36, 556 (1947)*

[12] Elio Passaglia and Paul J. Shouse, Recommended Method of use

of standard light-sensitive paper for calibrating carbon arcs

used in testing textiles for colorfastness to light,

National Bureau of Standards Miscellaneous Publication

260-15 (1967).

[13] American Association of Textile Chemists and Colorists

Technical Manual B-72, Colorfastness to Light:

Carbon arc lamp, continuous light Method 16A-1964.

[14] William R. Martin, Jr. (AATCC) Letter dated September l4, 1966

to Elio Passaglia (NBS).

[15] Paul J. Shouse, Standard light-sensitive paper for use in

testing textiles for colorfastness to light, National Bureau

of Standards, Letter Circular LC IO36 (June 1965).

[16] J. L. Michaelson, Construction of the General Electric

Recording Spectrophotometer, J. Optical Soc. America 28 ,

365 (1938).

25

USC O MM—DC— N BS
APPENDIX

COLOR DIFFERENCE EQUATIONS

Color Difference in NBS Units References A2, A3, AN- and A5

1. Chromatic ity co-ordinates

x X

and Y

= Y

X+Y+Z ^ X+Y+Z

2. Hunter chromatic ity co-ordinates

2 .4266 x - l.3631y - 0.3214

x + 2.2633y

4- 1.1054

0.5710 x - 1.2447,7 - 0.5708

x + 2.2633y + 1.1054

2

'• 2a = (a

2

- a

± y

_2

__lA

= (32

- P 1

)

£

- ( Y

i + Q AA

)

a(y

1/2 )= y//2

- y//2

4a. Color difference when Y^ and Y are expressed as decimals

_!A .2 2 1/2 2 2 1/2

AE 1

= {[700 Y (2a + 2$ ) ] + [120 A(r^)] }

4b. Color difference when Y and Y are expressed in percent

_l/4 2 2 1/2 2 1/2 2 1/2

AE - {[221 Y (2a + 2£ ) ] + [12 A(Y )] }

26
II. Color Difference in Scofield-Hunter Units References /A2-A9

la. When X, Y, and Z are expressed as

L = 1/2100 Y

'

a = 175 (1.02 x - y) y

" 1//2

b

L

* 70 (Y - 0.847 z) Y

-1/

2

lb. When X , X, and Z are expressed in

L 10 Y

1/

2

aL

= 17.5 (1.02 x-y) y

“ i/2

b

L

= 7.0 (Y - 0.847 z) Y‘

l/2

2. AL = L

2

" L

1

AaT = aL2

“ aLl

b

L2

“ b

Ll

3- AEg =

CM

1

—

1

1

—

1

CM + gCM +

CM 1

1 I

27
III. Color Difference Calculated by the Cube-Root Relation of Glasser,

McKinney, Reilly, and Schnelle References A4, A10

1. R = 1.02 X

G = Y

B = O. 8V7 Z

2 . A(R1/3

) . r^/3 - r!/3

a(G-1/3)= 4/3. 0V3

A(B1// -’) = Bg/3 . bV3

3a. When X , Y, and Z are expressed as decimals

&L - 174 a(g

1^ 3

)

Aa = 492 [A(R

X'/3

) - a(g1//3

)]

Ab = 196.5 [A(G

1//3

) - A (B

1/3

)]

3b. When X , Y, and Z are >expressed in percent

AL = 25.29 a(g1//3

) Aa = 106.0 [a(r

1//3

) - A(G1/3

)J

Ab = 42.3^ [A(G1//3

) - A(B1/3

)]

4. = [(AL ) 2 + (Aa) 2 +

^“ro 11 H ro

28
IV. Color Difference in MacAdam units Calculated by the Modified Formula

of Friele, MacAdam} and Chickering as presented by Billmeyer

References All - A15

X, Y, and Z are to be expressed in percent

1. P = 0.724 X + 0.382Y - 0.098Z

Q

= -0.48 X + 1.37 Y + 0.1276Z

S = 0.686 z

2. AP

YH

AS

P - P

2 1

Q - Q ^2 YL

S

2

- s

.-6 / 2

3. a

4- = 17.3 x

10“" (Pj + Q^) [1 + 2.73 0^ (P^ + Q^)"

1 ]" 1

3.O98 x Kf4(S^ + 0.2015 Y^)

4. = O.55669 + 0.04934 Y - 0.82575 x 10' 3 Y

4

+ 0.79172 x 10

" 5 Y

3

- 0.30087 x 10

' 7 Y

4

K. = 0.17548 + 0.027556 Y, - 0.57262 x lo" 3

y

4

+ 0.63893 x

10" 5 Y^ - 0.26731 x 10

_7

Y

4

29
5 . AL

2 = (p/pp + <7 + ‘4 2

1//2

^2 = 0.279 Alj/a

6. AC

rg

= (^ap - p^q) (p? + i^y1/2

AC

ybVi = S

1

AL

X

(P

2

+ ti2 )" 1/E- AS

7- AC

X

= t(AC

rg

/a)2

+ (AC^/b)2

] 1^

AC =

11 w

H

AL = k

2

^

CO II [(AC)2

+ (AL)

2

] 1/2

30

COLOR DIFFERENCE REFERENCES

General References

A 1. I. Nimeroff, "Colorimetry", National Bureau of Standards, Monograph 104,

January 1968 .

A 2. D. B. Judd "Color in Business, Science and Industry", page 253-267,

John Wiley, New York 1952.

A3- D. B. Judd and G. W. Wyszecki "Color in Business, Science and Industry"

2nd Edition, pages 294-296, John Wiley, New York 1963 *

A 4. G. Wyszecki and W. S. Stiles, "Color Science: Concepts and Methods

quantitative Data and Formulas", pages 459-468, John Wiley,

New York 1967 .

A 5- F. W. Billmeyer and M. Saltzman "Principles of Color Technology",

John Wiley, New York 1966 .

Specific References

A 6. F. Scofield, National Paint, Varnish and Lacquer Assoc. Sci. Section

Circular 664 (July 1943)*

A 7 . R- S. Hunter, "Photoelectric color-difference meter", J. Opt. Soc.

Am. 38 , 66l (1948)

A 8 . R. S. Hunter, "Accuracy, precision, and stability of a new photoelectric

color-difference meter", J. Opt. Soc. Am. 38 , 1094 (1948).

A 9 . R. S. Hunter, "Photoelectric color-difference meter", J. Opt. Soc. Am.

48, 985 (1958).

A 10. L. G. Glasser, A. H. McKinney, C. D. Reilly

> and P. D. Schnelle

"Cube-root color coordinate system", J. Opt. Soc. Am. 48 , 738 (1958).

31
A 11. L. F. C. Friele "Further analysis of color-discrimination data"

J. Opt. Soc. Am. 55 , 1314 ( 1965 ).

A 12. L. F. G. Friele "Friele approximations for color metric coefficients"

J. Opt. Soc. Am. 56 , 259 (1966).

A13. D. L. MacAdam "Smoothed versions of Friele’s 1965 approximation for

color metric coefficients", J. Opt. Soc. Am. 56., 1784 ( 1966 ).

A l4. K. D. Chickering "Optimization of the MacAdam-modified Friele colordifference formula" J. Opt. Soc. Am. 57., 537 (1987)*

A 15- Fred W. Bilime yer, Jr. and Rodger Smith, "Optimized equations for

MacAdam color differences" Color Engineering page 28 (Nov. -Dec. 1967 ).

32
Table

1.

Color

Difference,

Change

in

Spectral

Reflectance

at

670

nm,

and

Cl

Tri-Stimulus

Value

Y

at

Different

Exposures

•rH

• H 00 O CO VO ON IT\ i'H ON P CM ON VO VO P O LTN P va ctf |<j on OO CM CO CO CO O VO K

It

rH H H rH H rH ! H O • • O

O • • • •

1 •

1

• OO

5

0

t

13

wp

/—

s

j j

1

1—1 ^ V OOr-s ON^. p va P OJ co '&a 0 0 *5a D—'feS. IP t— LTN H vo vo

1 CM H O CO CO • 3 d

CO • 00 • CO » P • co c— P P UN4-

•rH • CM • CM • 1—

1

• rH • rH • H O CO CM '

1

1

O CD vo -H* rH ON : o> rH C— CO

•rH PP LTN OJ -H- CO rH CO rH 'sa

-R PCO

CM C\J OJ CM ; oj CM CM O vo

ct5 &

• O• • • ! • •

i j * •

Lf\

1—l co

CO CO o

Pc a

K

o

0

c

vo

j

| P *—

X

*N /•—

N

0 CO ^ c—'Ba CO b-'sa CO « 'sa rH 00 LTN CO co-ea t— CO CO OJ VO • VO « D-P t— • D— • P • p • vo . . • LTN • LT\ CO O CM rH ON rH «H <f

' " ' ' V '

ON •

*

1—I HI 'gS. 07. O—

"

H CO 00 H VO

p- • ON • O

• O • pCVI OJ CM rH

• LTN ro H 00

'55. r-~s CO^. O CO LTN -6^

IT\ ON O • H OO

CM • VO O CO • On • 1—I • On

'—» CO'^-' CO*

\ —I,

( vo \A

o

rH

lO

Is3

00

rH

O* p-HO

VO

r—

1

0

1 LTN H

O

; • i°qH

CrH

O

o

CM

0 P w •rH •H • • P • 0 CJ

CD p t> 0 h p 0

O cd P 0 O p 3 0 SH a P CO (H O 0 > P

P

O

1.

For

calculation

of

ratios,

the

values

are

given

to

one

more

significant

digit

than

the

number

justified

by

the

sion

of

the

measurements.

2.

The

numbers

in

parentheses

indicate

the

coefficient

of

variation

(ratio

of

standard

deviation

to

mean

value)

single

observation

from

the

arithmetic

mean

of

the

10

observations

at

each

exposure.
Table

2

Color

Difference

In

Various

Units

at

Different

Exposures

o

•H-8

ps 13 if

-4

* r- ) oo CO OJ H 1 OJ ON 00 00 00 t— oo UA O VO

-4

* -4 CO UA 1 UA UA r

1 © * *» o ® UA O • • • rH H rH

1 rH rH

! rH H O

8 p

}

r H CD

l 4 SH >3 5 a) CD <L> 0) CO CO I—1 Cvj

-4

* rH a D— UN ! CO ) oo 9

0! (—1 <

o

O

•H UN OO© OJ

9

i rH

} • P ctf n •H oo -4 -4 Lf\ S o PQ

o

•rH

ctf PS

oo 13

H

IS

0

•H1 ir ii3

sUA

Lf\

o

VO

UA

O o

-4" oo

UN

00

VO

-4* o

OJUA

rHOO

LfA

OJ i—

13

i—

a; a

(

j

j

i

i

j i

s

i •H (D OO ON -4

"

\ -4 CH

* o -P o o OJ ! VO o oo ° 3 o 3

OJ

9 UA CO

• ® LT\

©

i CO

• H

co K rH H *—

! H H OJ*

vo

-4-

t—H

On

• UA

4

UA 00

UA

OO O

oo

L!A o

^_H-

• • • D—

ON VO rH oo f o OJ

-4

* VO OO ON H ^ oo

oo ! UA ~4

- VO 1 ^ ; cvj

« • • © • • rH H rH rH

j H i OJ

ON ! UA OO ! cvj rH i CO ON H oo j CO O UA

-4

“ UN -4

-

i -4

" LO UN • O

© e i & «

i

i »

41

I < CO H

ON ^5.

i: H .

i! T

CO

H CQ 13 e

3-4"

• OJ

H

OOON

•

CVJ

O

VOO• oo

'

•

oo

UA

OJ

• OO

!

'

!

r o

o

VO

• oo r— t H

CO" |

1

- -

i

•8

t> 0) O

•H • 3

-p > o

co fri o E

CVI H VO VO o c—

(4 a) PS Q X

Pa OQ t— ON

® rH

® oo

• LT\

9

t

<P

cj . Ch

C£j

i—

rH rH H 3 0) JU -P O S CO o
Table 3

Calculated

Color

Differences

and

Related

Quantities 3

ion onO«o

•HIs« o

ft- CO ft- «H

0) ftft

CO<f

13

-4

on

CM• o

•Hs

ft

CMOLfN• iH»O

•HIs

ft

13

on

on

on

LfN• o jiiI i 1 1 on rH CO ' -4 )S

l>- ft- o LTV VO CO , ON rH CM

•H • • • • • • • Is

ft

rH rH rH ! H j

CM CVJ CM

If

coON

-4oO

•Hs

ft

CM

rH

H

43

H &o

CD

coa&

CO

CO

onoo

on

It

rH

c—

oo

CM

-4O

LfN

VO & H 1 ° ! CO

CM LfN ft- • 1 -4- ? • LfN• ; ltn• LfN• o : CO on LfN LfN O

CO rH oo CO rH CO rH CO ft- CO ! CO ON ON O

LfN ft- rH

co 8n

ono

CM 8! on

CM

LfN on 3*

ION H

-4

CO

on j CO

co

on

ft- o• ~4*

co

H

O

CM

i-

rH -4" ON o H o CO LPv CM -4" CO H -4* • • • • • • • r4* LPv , ^ LPv VO VO

2)o CM

CO

CM -4

CM

CM

e'- enON

-4

rH83P

HO

CD ft£O

0)§

ft

CD §I CO

rQ

bOa

•H

ctf Ph

<D rH8

•HO

CDP

ft

ft <

-p

CO0

ft

CJo

!hft

CO

cS ft

CD Isp

CD8

coO

ft &
LEGENDS FOR FIGURES

Figure 1. Average specimen score (circles) as a function of exposure

time

Vertical coordinate: average specimen score Horizontal coordinate: exposure time

Frequency distribution (crosses) of individual specimen scores

Vertical coordinate: individual specimen score Horizontal coordinate: number of specimens having the given

individual specimen score (measured in each case from a vertical

zero axis through the average specimen score at each exposure time)

The individual specimen numbers near each cross represent position

around the drum during exposure.

Figure 2. Average observer score (circles) as a function of exposure

time

Vertical coordinate: average observer score Horizontal coordinate: exposure time

Frequency distribution (crosses) of individual observer scores

Vertical coordinate: individual observer score Horizontal coordinate: number of observers reporting the given

individual observer score (measured in each case from a vertical

zero axis through the average observer score at each exposure time)

The individual observer numbers are shown near each cross.

Figure 3* Spectral reflectance as a function of wave length

The number of SFH of exposure is shown near each curve. The paper is a specimen of Lot 700a.

The wool is a specimen of the 1957 Lot of L-4 Wool.

Figure 4. Color difference as a function of time of exposure (upper

curve, upper abscissa) or of square root of time of exposure (lower

curve, lower abscissa).
NO.

OF

SPECIMENS

HAVING A

GIVEN

SCORE

oo

CO

co oo co oo co

co

CO

oo

CO

oo

oo

I 3dOOS N3lAJI33dS

SFH
3UOOS U3/\U3$B0

SFH
<d

CO

CD

CD

LO

CD

CD

CD

LO

LO

CD

CD

LO

CD

LO

or-0

30N\/±D31J3d lVd_LD3dS

uuu
LO

fr 3V mQVW

CO

LO

'3V S8N

I