BS EN ISO 787-25:2019 pdf free.General methods of test for pigments and extenders.
The test pigment and an agreed reference pigment are dispersed in a particular test medium, consisting of a mixture of an alkyd resin and fumed silica, using an automatic muller. From the dispersions of the two pigments, specimens on suitable substrates are prepared. The tristimulus values of the specimens are measured as described in ISO 18314-1 and from these, the appropriate colour characteristics (relative hue and amount of relative hue for black and white pigments). Lightness, hue, chroma and total colour difference for coloured pigments are calculated as described in ISO 11664-4.The preferred test medium (see Table 1 and Table 2 for quantities) is prepared as follows. Mix 97 parts by mass of alkyd resin (5.1) and 3 parts by mass of fumed silica (5.2) well. Take care that no silica is lost by evolution of dust. Disperse the mixture twice on a triple-roll mill according to ISO 8780-6. Another test medium may be agreed between the interested parties. This shall be indicated in the test report.Spectrometer or tristimulus colorimeter as specified in ISO 18314-1 and complying with the following requirements. a) Accuracy A spectrometer shall provide reflectance values to five decimal places; a tristimulus colorimeter shall provide tristimulus values to three decimal places. b) Calibration and zero adjustment The instrument should preferably be such that it can be adjusted by using a suitable black standard so that the data for the tristimulus values are close to zero. If direct adjustment cannot be performed, the readings for the black standard shall be subtracted from the values for the test specimens. . The black standard used for the zero adjustment shall be a highly efficient light trap as shown in Figure 1 and having the following dimensions:A≥diameter of instrument sample port +5 mm; B≥80mm; C≥70 mm.The black standard shall have a non-gloss black interior and the bottom shall be covered with a mat black coating. Standard deviation of tristimulus values c)The standard deviation σr for consecutive measurements of tristimulus values shall be < 0,005. It shall be calculated from 20 measurements of tristimulus values without changing the position of a test specimen having a tristimulus value Y of about 0,5.BS EN ISO 787-25 pdf download.