Standard Test Method for Measurement of Light Reflectance Value and Small Color Differences Between Pieces of Ceramic Tile
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:
FIG. 2 Example of a Product Mix Used on a 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 according to this test method, should give excellent reproducibility with a standard deviation of not more than σ = ±0.15 units. LRV should also give excellent reproducibility when used for solid colored tile based on the relationship between LRV and either the Y tristimulus or L value. However, LRV reproducibility for multicolored, speckled, or textured surface tile will be dependent upon the degree of variation of the tile specimen, and will require a different measurement procedure to minimize the impact of the variation.
5.6 The test method requires the use of multiple illuminants for the determination of color difference between solid-colored tiles. Evaluation under incandescent, fluorescent and daylight illuminant conditions ensure the color differences calculated between a test and reference specimen account for the possible occurrence of metamerism.
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 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, 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.
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