ASTM

Until the America Society for Testing Materials (ASTM) started testing the performance of artists paints manufacturers took advantage of artist inexperience with paint chemistry to sell products that were poor yet could be labeled as permanent on the tube. Various star or other rating systems touted bad pigments as good. This was because the manufacturers were doing their own rating, and no-one was checking the accuracy of claims. Enter the ASTM. They were independent and had no vested interest in selling any of the products, but they were interested in consistent standards. In order for a manufacturer to quote ASTM ratings for colors they are required to adopt certain strict standards. The artist can buy with confidence that the information on the tube is correct. ASTM standards divide pigments into 5 levels. Only the first 3 are considered suitable by authorities for artists use, and I personally would not recommend using anything other than ASTM 1 and ASTM 2. Since the adoption of ASTM standards by many of the worlds best manufacturers paint quality has improved markedly