ASTM C609-23

Standard Test Method for Measurement of Light Reflectance Value and Small Color Differences Between Pieces of Ceramic Tile

SIGNIFICANCE AND USE
5.1 This test method describes the means of determining the LRV of a tile specimen. Certain building codes require the use of materials rated by LRV. Application of this test method provides the means for rating ceramic tile. LRVs reported for ceramic tile should include reference to the observer and illuminant for which the rating is valid.  
5.2 LRV is a property dependent on the overall color of a tile specimen. Control of LRV is achieved through control of color and adherence to color specifications will govern the acceptability of a product with respect to LRV. Therefore, a product cannot be judged as having an unacceptable LRV unless the color of the product is found to be unacceptable.  
5.3 Mixtures of several tile products are commonly installed on a surface, requiring a means to calculate LRV for a product mix. The rating obtained for an individual tile product can be used to calculate the LRV for a product mix using the following equation:
   where:  
  n  =  number of products included in the mix,    p1 to n  =  the proportion of the surface area taken up by each product; the sum of p1 to pn must equal one), and   LRV1 to n  =  the LRV for each product used.    For example, a mixture of two products is used on a surface. Two thirds of the surface area is covered by product A with a LRV of 75 %, and one third of the surface is covered by product B with an LRV of 60 % (see Fig. 2). Using the equation, the product mix is found to have an LRV of 70 %.  
FIG. 2 Example of Product Mix Used on Surface
5.4 The test method described herein provides instrumental means as the basis for judging color difference. Magnitude of color difference between pairs of ceramic tile can be determined and expressed in numerical terms.  
5.5 Based on interlaboratory investigation,3 color difference ΔE  of plain-colored tile, if determined in accordance with this test method, should give excellent reproducibility with a standard deviation of not more than σ = ±...
SCOPE
1.1 This test method covers the measurement of Light Reflectance Value (LRV) and visually small color difference between pieces of glazed or unglazed ceramic tile, using any spectrophotometer that meets the requirements specified in the test method. LRV and the magnitude and direction of the color difference are expressed numerically, with sufficient accuracy for use in product specification.  
1.2 LRV may be measured for either solid-colored tile or tile having a multicolored, speckled, or textured surface. For tile that are not solid-colored, an average reading should be obtained from multiple measurements taken in a pattern representative of the overall sample as described in 9.2 of this test method. Small color difference between tiles should only be measured for solid-color tiles. Small color difference between tile that have a multicolored, speckled, or textured surface are not valid.  
1.3 For solid colored tile, a comparison of the test specimen and reference specimen should be made under incandescent, fluorescent and daylight illuminant conditions. The use of multiple illuminants allows the color difference measurement to be made without the risk of wrongly accepting a match when the tiles being compared are metamers (see 3.1.4).  
1.4 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are provided for information only and are not considered standard.  
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standard...

General Information

• Status: Published
• Publication Date: 30-Sep-2023
• ICS: 91.100.25 - Terracotta building products
• Technical Committee: C21 - Ceramic Whitewares and Related Products
• Drafting Committee: C21.06 - Ceramic Tile

Relations

• Replaces: ASTM C609-20 - Standard Test Method for Measurement of Light Reflectance Value and Small Color Differences Between Pieces of Ceramic Tile
• Effective Date: 01-Oct-2023

Overview

ASTM C609-23 - Standard Test Method for Measurement of Light Reflectance Value and Small Color Differences Between Pieces of Ceramic Tile - is an internationally recognized method developed by ASTM International. This standard specifies procedures for the quantitative measurement of Light Reflectance Value (LRV) and the detection of small color differences in both glazed and unglazed ceramic tiles. By employing spectrophotometric instruments, this test method ensures accurate, repeatable, and consistent assessment of tile color and reflectance. The standard is relevant for manufacturers, specifiers, and regulatory agencies requiring reliable color and reflectance data for ceramic tiles, which are critical properties in both aesthetic and functional building applications.

Key Topics

• Light Reflectance Value (LRV): Measures the percentage of visible light reflected from a tile surface. LRV is a vital factor in architectural and design decisions, supporting compliance with building codes and accessibility guidelines.
• Color Difference Measurement: Quantifies visually small differences between solid-colored tiles under various illuminant conditions (daylight, incandescent, fluorescent), helping to ensure color consistency and prevent issues related to metamerism.
• Applicable Tile Types: The method accommodates both solid-colored tiles and those with multicolored, speckled, or textured surfaces, though color difference evaluation is limited to uniform color samples.
• Use of Spectrophotometers: Outlines requirements for instrument performance and calibration. Accurate LRV and color difference assessment depends on repeatable, standardized instrument settings and reference materials.
• Product Mix Assessment: Provides calculation for LRV when multiple tile products are used within a single installation, ensuring comprehensive evaluation of the overall visual impact.
• Reporting & Precision: Describes necessary details to document, including description of specimens, instrument settings, illuminants, and individual measurements. Emphasizes reproducibility and reliability of results.

Applications

ASTM C609-23 is used widely by:

• Ceramic Tile Manufacturers: To control color and LRV during production, ensuring products meet specified tolerances for both visual appearance and code compliance.
• Architects and Designers: To select tile materials with appropriate light reflectance values, optimizing lighting conditions, aesthetic intent, and accessibility in interior or exterior spaces.
• Quality Control Laboratories: To conduct regular inspections of production batches, verifying color consistency and product acceptability.
• Building Code Authorities: For verifying compliance with regulations that require surfaces to meet minimum or maximum LRV values for safety or accessibility, such as in public or commercial spaces.
• Installers and Specifiers: To assess and document the combined LRV of mixed-tile installations, achieving desired design effects while adhering to project requirements.

This standard helps ensure that ceramic tiles used in construction and design have consistent, measurable visual properties and are compliant with industry best practices and applicable regulations.

Related Standards

• ASTM C242: Terminology of Ceramic Whitewares and Related Products
• ASTM D2244: Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Color Coordinates
• ASTM E259: Practice for Preparation of Pressed Powder White Reflectance Factor Transfer Standards
• ASTM E284: Terminology of Appearance

These referenced standards provide foundational definitions, measurement practices, and guidance for color and appearance testing, supporting the accurate and standardized application of ASTM C609-23 in the ceramic tile industry.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C609 − 23
Standard Test Method for
Measurement of Light Reflectance Value and Small Color
Differences Between Pieces of Ceramic Tile
This standard is issued under the fixed designation C609; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.1 This test method covers the measurement of Light
Reflectance Value (LRV) and visually small color difference
2. Referenced Documents
between pieces of glazed or unglazed ceramic tile, using any
2.1 ASTM Standards:
spectrophotometer that meets the requirements specified in the
C242 Terminology of Ceramic Whitewares and Related
test method. LRV and the magnitude and direction of the color
Products
difference are expressed numerically, with sufficient accuracy
D2244 Practice for Calculation of Color Tolerances and
for use in product specification.
Color Differences from Instrumentally Measured Color
1.2 LRV may be measured for either solid-colored tile or
Coordinates
tile having a multicolored, speckled, or textured surface. For
E284 Terminology of Appearance
tile that are not solid-colored, an average reading should be
obtained from multiple measurements taken in a pattern
3. Terminology
representative of the overall sample as described in 9.2 of this
3.1 Definitions:
test method. Small color difference between tiles should only
*
3.1.1 color difference, ΔE and ΔE , n—the vector sum of
H
be measured for solid-color tiles. Small color difference * * * *
the three component differences ΔL , Δa , and Δb for ΔE and
between tile that have a multicolored, speckled, or textured
ΔL , Δa , Δb for ΔE . The superscript * indicates color
H H H H
surface are not valid.
difference based on the use of CIELAB color space equations,
1.3 For solid colored tile, a comparison of the test specimen
while the subscript H indicates color difference based on the
and reference specimen should be made under incandescent, use of the Hunter equations. ΔE is expressed in units of judds,
H
*
fluorescent and daylight illuminant conditions. The use of
while ΔE is a unit-less value. Either form of the ΔE can be
multiple illuminants allows the color difference measurement
solved for using the equation shown in 10.3. For both the
to be made without the risk of wrongly accepting a match when
CIELAB and Hunter equations, the values ΔL, Δa, and Δb are
the tiles being compared are metamers (see 3.1.4).
obtained by calculating the component differences as follows:
1.4 The values stated in inch-pound units are to be regarded ΔL 5 L 2 L
t r
as standard. The values given in parentheses are provided for Δa 5 a 2 a
t r
Δb 5 b 2 b
information only and are not considered standard.
t r
1.5 This standard does not purport to address all of the
where:
safety concerns, if any, associated with its use. It is the
t = test specimen, and
responsibility of the user of this standard to establish appro-
r = reference specimen.
priate safety, health, and environmental practices and deter-
The quantity ΔE has a positive value and it describes the
mine the applicability of regulatory limitations prior to use.
magnitude but not the direction of color difference between the
1.6 This international standard was developed in accor-
test specimen and the reference specimen. The direction of
dance with internationally recognized principles on standard-
color difference depends upon the algebraic signs of the
ization established in the Decision on Principles for the
components ΔL, Δa, and Δb. A positive ΔL value means that
Development of International Standards, Guides and Recom-
the test specimen is lighter than the reference against which it
is being compared, and a negative ΔL value means that the test
This test method is under the jurisdiction of ASTM Committee C21 on Ceramic
Whitewares and Related Products and is the direct responsibility of Subcommittee
C21.06 on Ceramic Tile. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Oct. 1, 2023. Published October 2023. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1967. Last previous edition approved in 2020 as C609 – 20. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/C0609-23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C609 − 23
specimen is darker. However, the algebraic signs of chroma- 3.1.8 spectrophotometric, n—measurement of the spectral
ticity components, Δa and Δb, do not convey an easily reflectance or transmittance curve of a material.
visualized difference in color attributes and can best be
3.1.9 standard, n—the plaque or other media of established
visualized by plotting the corresponding points in the chroma-
tristimulus value, against which standardization of the instru-
ticity plane.
ment is made.
3.1.2 color space, n—the colors of opaque specimens such
3.1.10 test specimen, n—any piece of tile whose LRV or
as ceramic tile are described in terms of three color scales L, a,
color difference from a reference specimen is to be evaluated.
and b. Scale L is a measure of lightness, a is a measure of
3.1.11 tile, n—see Terminology C242.
redness or greenness, and b is a measure of yellowness or
blueness. The units for each of the three scales are so chosen
4. Summary of Test Method
that they represent equally perceptible color differences. The
4.1 This test method explains the technique for measuring
interrelation of these color scales is more readily visualized if
the LRV and color of tile specimens with a spectrophotometric
the scales are represented geometrically as the three mutually
instrument that meets the specified requirements. Such instru-
perpendicular axes of a three-dimensional color space, with the
ments should give results comparable to differences observed
L axis in the vertical direction, the positive a axis (redness) to
by the human eye, and yield for each color a unique, three-
the right, and the positive b axis (yellowness) in a counter-
number characterization, having known relationship to the
clockwise direction from the positive a axis (see Fig. 1).
tristimulus values X, Y, and Z.
4.2 Spectrophotometic measurement systems commonly
provide measurement data in a variety of color units and allow
for automatic conversion of data from one color system to
another. Select equations are included in this test method for
*
manual determination of LRV from Y, L , or L . Equations are
H
* * *
also provided for calculation of L , a , b , and L , a and b
H H H
from tristimulus values X, Y, and Z. The algebraic differences in
L, a, and b values, between any two specimens, are then used
to calculate the color difference, ΔE. If manual calculations are
required, consult the instrument supplier for conversions not
provided within this test method.
4.3 The complete description of the amount and direction of
a color difference between any two pieces of solid colored tile
can be given simply as the three respective differences between
the pairs of values for L, a, and b. For some purposes, ΔE alone
provides enough information, since its magnitude gives a fairly
good correlation with human opinions about the size of a color
difference.
4.4 To protect against approval of a metameric color match,
FIG. 1 Three-dimensional Color Space
multiple illuminates must be used when evaluating color
difference between solid colored tiles. A test specimen needs to
prove suitable with respect to a reference specimen under
3.1.3 light reflectance value, (LRV), n—the luminance factor
incandescent, fluorescent and daylight illuminant conditions in
Y, of a sample expressed as a percent. Thus, a Y value of 70
order to be judged as acceptable.
would equate to an LRV of 70 %. The LRV indicates the
portion of light cast on a sample that is not absorbed.
5. Significance and Use
3.1.4 metamers, n—see Terminology E284.
5.1 This test method describes the means of determining the
3.1.5 reference specimen, n—any tile for which a match is
LRV of a tile specimen. Certain building codes require the use
desired.
of materials rated by LRV. Application of this test method
provides the means for rating ceramic tile. LRVs reported for
3.1.6 repeatability, n—the standard deviation of results
ceramic tile should include reference to the observer and
obtained by the same operator using the same instrument in
illuminant for which the rating is valid.
successive measurements.
5.2 LRV is a property dependent on the overall color of a
3.1.7 reproducibility, n—the standard deviation of results
tile specimen. Control of LRV is achieved through control of
obtained by different operators using the same or different
color and adherence to color specifications will govern the
types of instruments in different laboratories.
acceptability of a product with respect to LRV. Therefore, a
Illing, A. M., Balinkin, I., “Precision in Measurement of Small Color
Differences,” American Ceramic Society Bulletin, Vol 44, No. 12, 1965, pp. Billmeyer, F.W. Jr., Saltzman, M., Principles of Color Technology, 2nd Edition,
956–962. John Wiley & Sons, Inc., New York, NY, 1981, p. 78, 85.
C609 − 23
6. Apparatus
6.1 Type of Instrument for LRV Measurement—Any color-
measuring spectrophotometric instrument capable of yielding
data that can be transformed mathematically into the Interna-
tional Commission of Illumination (CIE) tristimulus values X,
Y, and Z may be used. It must have a color difference, ΔE,
repeatability (see 3.1.6) of σ = 60.2 units or less, based on five
independent measurements. The well-known standard devia-
tion equation shown as follows is used to calculate the standard
deviation.
½
σ 5 F X 2 X /N (2)
@ #
~ !
(j j j
FIG. 2 Example of Product Mix Used on Surface
6.2 Type of Instrument for Color Measurement—For the
measurement of solid colored tile, the spectrophotometric
measurement system must meet all of the requirements for
LRV measurement and be capable of yielding tristimulus
product cannot be judged as having an unacceptable LRV
values X, Y, and Z for daylight, incandescent, and fluorescent
unless the color of the product is found to be unacceptable.
illuminants.
5.3 Mixtures of several tile products are commonly installed
6.3 Instrument Setup—For measurement of LRV and color
on a surface, requiring a means to calculate LRV for a product
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C609 − 20 C609 − 23
Standard Test Method for
Measurement of Light Reflectance Value and Small Color
Differences Between Pieces of Ceramic Tile
This standard is issued under the fixed designation C609; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the measurement of Light Reflectance Value (LRV) and visually small color difference between pieces
of glazed or unglazed ceramic tile, using any spectrophotometer that meets the requirements specified in the test method. LRV and
the magnitude and direction of the color difference are expressed numerically, with sufficient accuracy for use in product
specification.
1.2 LRV may be measured for either solid-colored tile or tile having a multicolored, speckled, or textured surface. For tile that
are not solid-colored, an average reading should be obtained from multiple measurements taken in a pattern representative of the
overall sample as described in 9.2 of this test method. Small color difference between tiles should only be measured for solid-color
tiles. Small color difference between tile that have a multicolored, speckled, or textured surface are not valid.
1.3 For solid colored tile, a comparison of the test specimen and reference specimen should be made under incandescent,
fluorescent and daylight illuminant conditions. The use of multiple illuminants allows the color difference measurement to be made
without the risk of wrongly accepting a match when the tiles being compared are metamers (see 3.1.4).
1.4 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are provided for
information only and are not considered standard.
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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C242 Terminology of Ceramic Whitewares and Related Products
D2244 Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Color Coordinates
This test method is under the jurisdiction of ASTM Committee C21 on Ceramic Whitewares and Related Products and is the direct responsibility of Subcommittee C21.06
on Ceramic Tile.
Current edition approved April 1, 2020Oct. 1, 2023. Published April 2020October 2023. Originally approved in 1967. Last previous edition approved in 20192020 as
C609 – 07 (2019).C609 – 20. DOI: 10.1520/C0609-20.10.1520/C0609-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C609 − 23
E259 Practice for Preparation of Pressed Powder White Reflectance Factor Transfer Standards for Hemispherical and
Bi-Directional Geometries
E284 Terminology of Appearance
3. Terminology
3.1 Definitions:
* * * * *
3.1.1 color difference, ΔE and ΔE , n—the vector sum of the three component differences ΔL , Δa , and Δb for ΔE and ΔL ,
H H
Δa , Δb for ΔE . The superscript * indicates color difference based on the use of CIELAB color space equations, while the
H H H
*
subscript H indicates color difference based on the use of the Hunter equations. ΔE is expressed in units of judds, while ΔE is
H
a unit-less value. Either form of the ΔE can be solved for using the equation shown in 10.3. For both the CIELAB and Hunter
equations, the values ΔL, Δa, and Δb are obtained by calculating the component differences as follows:
ΔL 5 L 2 L
t r
Δa 5 a 2 a
t r
Δb 5 b 2 b
t r
where:
t = test specimen, and
r = reference specimen.
The quantity ΔE has a positive value and it describes the magnitude but not the direction of color difference between the test
specimen and the reference specimen. The direction of color difference depends upon the algebraic signs of the components ΔL,
Δa, and Δb. A positive ΔL value means that the test specimen is lighter than the reference against which it is being compared, and
a negative ΔL value means that the test specimen is darker. However, the algebraic signs of chromaticity components, Δa and Δb,
do not convey an easily visualized difference in color attributes and can best be visualized by plotting the corresponding points
in the chromaticity plane.
3.1.2 color space, n—the colors of opaque specimens such as ceramic tile are described in terms of three color scales L, a, and
b. Scale L is a measure of lightness, a is a measure of redness or greenness, and b is a measure of yellowness or blueness. The
units for each of the three scales are so chosen 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 L axis in the vertical direction, the positive a axis (redness) to the right, and the positive
b axis (yellowness) in a counterclockwise direction from the positive a axis (see Fig. 1).
FIG. 1 Three-dimensional Color Space
Illing, A. M., Balinkin, I., “Precision in Measurement of Small Color Differences,” American Ceramic Society Bulletin, Vol 44, No. 12, 1965, pp. 956–962.
C609 − 23
3.1.3 light reflectance value, (LRV), n—the luminance factor Y, of a sample expressed as a percent. Thus, a Y value of 70 would
equate to an LRV of 70 %. The LRV indicates the portion of light cast on a sample that is not absorbed.
3.1.4 metamers, n—see Terminology E284.
3.1.5 reference specimen, n—any tile for which a match is desired.
3.1.6 repeatability, n—the standard deviation of results obtained by the same operator using the same instrument in successive
measurements.
3.1.7 reproducibility, n—the standard deviation of results obtained by different operators using the same or different types of
instruments in different laboratories.
3.1.8 spectrophotometric, n—measurement of the spectral reflectance or transmittance curve of a material.
3.1.9 standard, n—the plaque or other media of established tristimulus value, against which standardization of the instrument is
made.
3.1.10 test specimen, n—any piece of tile whose LRV or color difference from a reference specimen is to be evaluated.
3.1.11 tile, n—see Terminology C242.
3.1.11 spectrophotometric, n—measurement of the spectral reflectance or transmittance curve of a material.
4. Summary of Test Method
4.1 This test method explains the technique for measuring the LRV and color of tile specimens with a spectrophotometric
instrument that meets the specified requirements. Such instruments should give results comparable to differences observed by the
human eye, and yield for each color a unique, three-number characterization, having known relationship to the tristimulus values
X, Y, and Z.
4.2 Spectrophotometic measurement systems commonly provide measurement data in a variety of color units and allow for
automatic conversion of data from one color system to another. Select equations are included in this test method for manual
* * * *
determination of LRV from Y, L , or L . Equations are also provided for calculation of L , a , b , and L , a and b from
H H H H
tristimulus values X, Y, and Z. The algebraic differences in L, a, and b values, between any two specimens, are then used to
calculate the color difference, ΔE. If manual calculations are required, consult the instrument supplier for conversions not provided
within this test method.
4.3 The complete description of the amount and direction of a color difference between any two pieces of solid colored tile can
be given simply as the three respective differences between the pairs of values for L, a, and b. For some purposes, ΔE alone
provides enough information, since its magnitude gives a fairly good correlation with human opinions about the size of a color
difference.
4.4 To protect against approval of a metameric color match, multiple illuminates must be used when evaluating color difference
between solid colored tiles. A test specimen needs to prove suitable with respect to a reference specimen under incandescent,
fluorescent and daylight illuminant conditions in order to be judged as acceptable.
5. Significance and Use
5.1 This test method describes the means of determining the LRV of a tile specimen. Certain building codes require the use of
materials rated by LRV. Application of this test method provides the means for rating ceramic tile. LRVs reported for ceramic tile
should include reference to the observer and illuminant for which the rating is valid.
Billmeyer, F.W. Jr., Saltzman, M., Principles of Color Technology, 2nd Edition, John Wiley & Sons, Inc., New York, NY, 1981, p. 78, 85.
C609 − 23
FIG. 2 Example of Product Mix Used on Surface
5.2 LRV is a property dependent on the overall color of a tile specimen. Control of LRV is achieved through control of color and
adherence to color specifications will govern the acceptability of a product with respect to LRV. Therefore, a product cannot be
judged as having an unacceptable LRV unless the color of the product is found to be unacceptable.
5.3 Mixtures of several tile products are commonly installed on a surface, requiring a means to calculate LRV for a product mix.
The rating obtained for an individual tile product can be used to calculate the LRV for a product mix using the following equation:
LRV 5 p LRV 1p LRV 1….1p LRV (1)
product mix ( 1 1 2 2 n n
where:
n = number of products included in the mix,
p = the proportion of the surface area taken up by each product; the sum of p to p must equal one), and
1 to n 1 n
LRV = the LRV for each product used.
1 to n
For example, a mixture of two products is used on a surface. Two thirds of the surface area is covered by product A with a LRV
of 75 %, and one third of the surface is covered by product B with an LRV of 60 % (see Fig. 2). Using the equation, the product
mix is found to have an LRV of 70 %.
5.4 The test method described herein provides instrumental means as the basis for judging color difference. Magnitude of color
difference between pairs of ceramic tile can be determined and expressed in numerical term
...