Napthol Red, the napthol pigments were first patented in 1911 and used initially as cotton dyes, then in the 1920's they were 'laked' (precipitating a dye with a metallic salt to stabilize it) and began to appear as artist's colours.
In masstone a luminous red which leans towards orange, described as slightly opaque by Michael, which means used thinly it is rather transparent and more thickly it is opaque, basically not truly transparent but not far off.
Powerful tinter and much more satisfying pink orange tints than you get with a Cadmium, they are brighter and warmer.
Almost an transparent alternative to Cadmium Red Light with better tints with white added.
High pigment load, a little goes a long way.
Pigment - PR188
Vehicle - Linseed Oil
Opacity - Slightly Opaque
Tint Power - High