GRAY SCALE

Evaluation of the color transfer and of the variation of color.
There are two kinds of gray scales: the first one is used to express an objective evaluation with regard to the transfer of color from the test-piece in examination to another material. The second scale is used to give a countable value to the variation of color, i.e. to the degradation, the color change of the test-piece, due to many factors as light, humidity, heat, etc.

Scale Type 1:

The gray scale for assessing color transfer is used during the measure of the color fastness of a certain material and of its resistance to the transfer on another material, by comparison with standard parameters, valid in every place and condition. The scale is composed of 10 pairs of plaques: a pair of identical white plaques, and 9 pairs made with a white plaque and a gray one, with the gray changing in intensity: different gray tones meaning different fastness. The two white plaques have fastness 5, the difference of color between them is zero. Fastness values from 4/5 to 1 correspond to pairs of plaques of which one is white and the other gray; the increasing contrast between the two plaques corresponds to a decreasing value of fastness, therefore the pair of plaques formed by the white and by the darker gray represents fastness 1. After having submitted a sample to test, the gray scale will serve to quantify the color transfer. So we compare the felt used for rubbing against a new one, then compare them to the 10 pairs forming the scale, we look for the pair with the contrast closest to the two felts. In this way we can give an objective evaluation of the quantity of color that was transferred to the felt during rubbing.

Scale type 2:

The gray scale for variation of color is used to compare the fastness of the color of a material and its resistance to agents that can change its intensity, as solar light, etc. The scale is composed of 5 pairs of gray plaques. In every pair, the difference of intensity and contrast between the plaques is variable, different contrast corresponds to different values of fastness, according to a scale that goes from 5 to 1. Fastness value 5 corresponds to an identical pair of plaques, with difference of color equal to zero. On the other hand, fastness value 1 corresponds to the highest degree of contrast between the two gray plaques. The use of this gray scale is analogous to the preceding one: after testing a piece of leather, this is compared with the original material and the contrast between the two is compared with the contrast inside every pair of the scale. In this way, we can give an objective evaluation of the color variation occurred.