There are concerns that cadmium yellows (PY 35, or cadmium sulphite) may fade over time, as has been observed in several paintings, although this pigment is rated as having excellent lightfastness (or 8;8;8 at BWS – Blue Wool Scale). There are reports of Van Gogh, Matisse and Munch works where the cadmium yellow turned into a milky-gray compound. Researchers have found that one variety of cadmium yellow becomes cadmium sulfate when it is exposed to excessive dampness and light, over decades. Some say this is problem that affects only the cadmium yellows produced before 1920, as the manufacturing process has changed since then. So, actual paints of such pigment would be stable. But, besides, there are the safety issues related to cadmium pigments. These questions may lead one to look for a substitute for cadmium yellow.
Unfortunately, there isn’t yet an ideal replacement. Others yellows usually fail in offering equivalent opacity and covering power.
Commonly, yellow pigments used as “substitutes” for PY 35 are: PY 74, PY 73 and PY 65. All of these three are labeled as being of low hazard.
PY 74, a “hansa” (or “azo”, or “arylide”) yellow, may be not entirely reliable: it’s rated as having just a good lightfastess (or, sometimes, a 7;6;5 at BWS).
PY 73 e PY 65 are the “azos” with better lightfastness. PY 73 ranges from reddish to greenish yellow. It’s not opaque as a cadmium. PY 65 tends to present a more reddish tone, and may be a bit more transparent than PY 73. I’ve tested Winsor Artist’s Yellow Deep, produced with PY 65, and it’s really a bright reddish yellow, nearly an orange, as can be seen in the photo. It’s nicely saturated.
Others oil paints that are produced with this pigment are Lefranc & Bourgeois Chrome Yellow Deep Hue and Williamsburg Permanent Yellow Deep.