ASTM C609-90(1995)
(Test Method)Standard Test Method for Measurement of Small Color Differences Between Ceramic Wall or Floor Tile
Standard Test Method for Measurement of Small Color Differences Between Ceramic Wall or Floor Tile
SCOPE
1.1 This test method covers the measurement of a visually small color difference between two pieces of solid-colored, glazed or unglazed ceramic tile, using any photoelectric instrument that meets the requirements specified in the test method. The amount and the direction of the color difference are expressed numerically, with sufficient accuracy for use in product specification.
1.2 This test method should not be used for determining small color differences between tile that have a multicolored, speckled, or textured surface, because the results may not be valid.
1.3 Color difference between specimens found to be metamers (see 3.2), by visual examination, can be accurately evaluated by spectrophotometric measurement only. Therefore, visual color comparison of test specimen and reference specimen should be made under incandescent light and under daylight fluorescent light before any instrumental measurement. If visual color difference under the two light sources is not of the same magnitude, the pair of tile must be considered metamers.
1.4 The values stated in inch-pound units are to be regarded as the standard. The values given in parentheses are for information only.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: C 609 – 90 (Reapproved 1995)
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Measurement of Small Color Differences Between Ceramic
Wall or Floor Tile
This standard is issued under the fixed designation C 609; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope Reflectance Factor Transfer Standards for Hemispherical
Geometry
1.1 This test method covers the measurement of a visually
E 284 Terminology of Appearance
small color difference between two pieces of solid-colored,
glazed or unglazed ceramic tile, using any photoelectric
3. Terminology
instrument that meets the requirements specified in the test
3.1 Definitions:
method. The amount and the direction of the color difference
3.1.1 color difference, DE—the vector sum of the three
are expressed numerically, with sufficient accuracy for use in
component differences DL, Da, and Db. It is expressed in units
product specification.
of judds and may be computed by the equation shown under
1.2 This test method should not be used for determining
9.7. The values DL, Da, and Db are obtained by calculating the
small color differences between tile that have a multicolored,
component differences as follows:
speckled, or textured surface, because the results may not be
valid. DL 5 L 2 L
t r
1.3 Color difference between specimens found to be metam-
Da 5 a 2 a
t r
ers (see 3.2), by visual examination, can be accurately evalu-
Db 5 b 2 b
t r
ated by spectrophotometric measurement only. Therefore, vi-
sual color comparison of test specimen and reference specimen
where:
should be made under incandescent light and under daylight t 5 test specimen, and
r 5 reference specimen.
fluorescent light before any instrumental measurement. If
The quantity DE has a positive value and it describes the
visual color difference under the two light sources is not of the
same magnitude, the pair of tile must be considered metamers. magnitude but not the direction of color difference between the
test specimen and the reference specimen. The direction of
1.4 The values stated in inch-pound units are to be regarded
color difference depends upon the algebraic signs of the
as the standard. The values given in parentheses are for
components DL, Da, and Db. A positive DL value means that
information only.
the test specimen is lighter than the reference against which it
1.5 This standard does not purport to address all of the
is being compared, and a negative DL value means that the test
safety concerns, if any, associated with its use. It is the
specimen is darker. However, the algebraic signs of chroma-
responsibility of the user of this standard to establish appro-
ticity components, Da and Db, do not convey an easily
priate safety and health practices and determine the applica-
visualized difference in color attributes and can best be
bility of regulatory limitations prior to use.
visualized by plotting the corresponding points in the chroma-
2. Referenced Documents 4
ticity plane.
2.1 ASTM Standards: 3.1.2 color space—the colors of opaque specimens such as
C 242 Terminology of Ceramic Whitewares and Related ceramic tile are described in terms of three color scales L, a,
Products and b. Scale L is a measure of lightness, a is a measure of
D 2244 Test Method for Calculation of Color Differences redness or greenness, and b is a measure of yellowness or
from Instrumentally Measured Color Coordinates blueness. The units for each of the three scales are so chosen
E 259 Practice for Preparation of Pressed Powder White that they represent equally perceptible color differences. The
interrelation of these color scales is more readily visualized if
the scales are represented geometrically as the three mutually
perpendicular axes of a three-dimensional color space, with the
This test method is under the jurisdiction of ASTM Committee C-21 on
L axis in the vertical direction, the positive a axis (redness) to
Ceramic Whitewares and Related Products and is the direct responsibility of
Subcommittee C21.06 on Ceramic Tile.
Current edition approved Dec. 28, 1990. Published February 1991. Originally
published as C 609 – 67. Last previous edition C 609 – 86. Illing, A. M., Balinkin, I., “Precision in Measurement of Small Color
Annual Book of ASTM Standards, Vol 15.02. Differences,” American Ceramic Society Bulletin, Vol 44, No. 12, 1965, pp.
Annual Book of ASTM Standards, Vol 06.01. 956–962.
C 609
the right, and the positive b axis (yellowness) in a counter- 4.4 The DE units of color difference are usually designated
clockwise direction from the positive a axis (see Fig. 1). as the National Institute of Standards and Technology (NIST)
3.1.3 metamers—See Terminology E 284. units of color difference, or simply as “judds.”
3.1.4 reference specimen—any tile for which a match is
5. Significance and Use
desired.
5.1 The test method described herein provides instrumental
3.1.5 repeatability—the standard deviation of results ob-
tained by the same operator using the same instrument in means as the basis for judging color difference. Magnitude of
color difference between pairs of ceramic tile can be deter-
successive measurements.
3.1.6 reproducibility—the standard deviation of results ob- mined and expressed in numerical terms.
5.2 Based on interlaboratory investigation, color difference
tained by different operators using the same or different types
of instruments in different laboratories. DE of plain-colored tile, if determined according to this test
method, should give excellent reproducibility with a standard
3.1.7 standard—the plaque or other media of established
tristimulus value, against which standardization of the instru- deviation of not more than s560.15 judds.
ment is made.
6. Apparatus
3.1.8 test specimen—any piece of tile whose color differ-
6.1 Type of Instrument—Any color-measuring instrument
ence from a reference specimen is to be evaluated.
either of the spectrophotometer or colorimeter type, capable of
3.1.9 tile—See Terminology C 242.
yielding data that can be transformed mathematically into the
4. Summary of Test Method
International Commission of Illumination (CIE) tristimulus
values X, Y, and Z, may be used. It must have a color difference,
4.1 This test method consists of measuring the color of tile
DE, repeatability (see 3.1.5) of s560.2 judds or less, based
specimens with any photoelectric instrument that meets the
on five independent measurements. The well-known standard
specified requirements. Such instruments should give results
deviation equation shown as follows is used to calculate the
comparable to differences observed by the human eye, and
standard deviation.
yield for each color a unique, three-number characterization,
2 ½
having known relationship to the tristimulus values X, Y, and Z.
s5 @( F ~X 2 X! /N# (1)
j j j
4.2 Some instruments read out directly in the L, a, and b
At the present time, spectrophotometers of the Hardy and
units which are required by this test method. Data from others
Cary type and colorimeters such as Gardner and Hunter color
must be converted to L, a, and b according to the equations
difference meters, the Color Eye, Colormaster and Chro-
given here, or others provided by the instrument supplier. The
mosorter, may be considered as suitable instruments.
algebraic differences in L, a, and b values, between any two
6.2 Spectral Characteristics—The spectral energy distribu-
specimens, are then used to calculate the color difference, DE.
tion of the light source and the spectral sensitivity of the
4.3 The complete description of the amount and direction of
receptor, if necessary, may have to be modified with properly
a color difference between any two pieces of tile can be given
selected filters to provide response functions approximating the
simply as the three respective differences between the pairs of
tristimulus functions of the CIE standard observer for illumi-
values for L, a, and b. For some purposes, DE alone provides
nant C.
enough information, since its magnitude gives a fairly good
correlation with human opinions about the size of a color
7. Standards
difference.
7.1 Primary Standard—The primary standard for reflec-
tance m
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