Permanence is the length of time a pigment retains its original color. Pigments must belightfast (not fade when exposed to daylight) and must not react chemically with other pigments and materials used in paintings nor the atmosphere.
A tube of paint is likely to have an indication of the permanency of the pigment on it. For example, the American Society for Testing and Materials (ASTM) rates lightfastness of pigments as: ASTM I = excellent; ASTM II = very good; ASTM III = may be satifactory if applied full strength.
