Blue Wool Scale is a way of measuring and calibrating the permenence of colouring pigments. Basically two identical pigment samples are created. One is placed in the dark as the stable original and the other is placed in the equivelent of sunlight for a 3 month period. The amount of fading is then measured by comparison to the original colour and a rating between 0 and 8 is awarded. Zero denotes extremely poor colour fastness whilst an Eight rating is deemed not to have altered from the original and thus credited as being lightfast and permanent.
The Encaustic Art Wax Block Colours are well placed using this scale & are generally deemed to have very good lightfastness.
Our own rating of 5 - 1 is used to show lightfastness. 5 is excellent & 3 is still good. This is the range within which the encaustic art colour source pigments fall. Mostly 5's, some 4's & a few 3's (mainly the Neons).