Naphthol AS Red is one of several napthols with similar names. We were surprised to find PR9 in oil paints currently available on the market - especially because these are primarily found in Cadmium Red imitations, and their lightfastness is not that good. This pigment has only moderate lightfastness- it is given an ASTM II in oil but depending on the paintmaker's pigment supplier, it may only get 5's in tints on the Blue wool scale. In watercolor, Bruce MacEvoy calls it very fugitive, and notes it is ASTM III in watercolor. However, his tests showed even worse performance- something like IV. We primarily noticed this pigment in student lines, and to make matters worse the PR9 was sometimes found alongside other pigments that also performed poorly.
Once again, Monona Rossol's writing raises awareness about potential serious health issues that could arise with this pigment, as it may metabolize to a carcinogen, so please consult her writing for more.
