Silica-coated white titanium pigments were developed by the Du Pont company with the following chalking resistance: r-902, rating 20+ and r-966 rating 32. Silica-coated molybdate oranges and chrome yellows are known to be resistant to light-induced darkening. The authors comment on an acid-resistant ultramarine pigment and on a nacreous lead white prepared in perfect hexagonal-shaped flakes.