ASTM D1544 test method for color of transparent liquids (Gardner color scale)
6. Report
6.1 Report the color as the number of the standard most closely matching the specimen. If more precise measurements are needed, report as either matching a standard or lighter or darker. Thus, between colors 5 and 6, the steps will be 5, 5+, 6-, and 6.
7. Precision and Bias
7.1 On the basis of a study in which one observer at each of 80 laboratories made duplicate determinations on four samples, the "between" and "within" standard deviations were found to be 0.5 and 0.1 color number, respectively. Based on these standard deviations, the following criteria should be used for judging the acceptability of results at the 95 % confidence level.
7.2 Repeatability - Two results obtained by a single operator should be considered suspect if they differ by more than two thirds of a color number.
7.3 Reproducibility - Two results, each of the mean of duplicate measurements, made by operators in different laboratories should be considered suspect if they differ by more than four thirds of a color number.
NOTE 1 - If desired, liquid standards matching the colors given in Table 1, in glass tubes similar to the sample tubes may be used. These may be filled with potassium chloroplatinate for the light colors and solutions of ferric chloride and cobalt chloride in hydrochloric acid for the darker colors. The specifications and approximate composition of these solutions are given in Test Method D1544 - 58 T. Many Glass Standards in current use do not conform to the values of Table 1.
NOTE 2 - The precision data were obtained using an instrument in which two standards are viewed simultaneously. There are other instruments available for color matching which would be expected to give similar results, but the statement above applies only to the instrument checked.
8. Keywords
8.1 glass filters; other measurements; transparent standards
