It is easy to find information on the internet about scientific research carried out on works by painters known as Van Gogh and Matisse. Cadmium yellow oil paint is undergoing chemical changes, turning the yellow paint into a pale compound, even changing the consistency of the paint in a salt. This seems to be concerns on the part of museums that see their capital degrade in a short time.
In the Just Paint article "Will Cadmium Always Be On The Palette? You mention it already:
"The difference between indoor and outdoor performance is thought to be due to the combination of environmental factors encountered outside; moisture, ultraviolet radiation and air. These cause bleaching induced by oxidation of the cadmium sulfide to cadmium sulfate. That is why the water permeable acrylic vehicle is prone to this effect, while cadmium pigments used in waterproof binders, such as rigid plastics, are not. "
Without delving into more details as each person can on the internet find expanded information on this matter and the reasons for my query, I raise my concerns.
1) What difference can there be between the pigments and the oil paints used in those art works and those that are commercialized today? PY 35 Cadmium Zinc Sulphide; and PY35: 1 with Barium according to the source. http://www.artiscreation.com.
In addition, I have not found any clarification on whether this unexpected effect of cadmium yellow, is also affecting the PY37, PO20, PR108.
2) Most artists are concerned about the permanence of their works, looking for materials and processes that allow their work to endure. From choosing the substrate, its preparation, the pigments resistant to light, etc. Why then, when mention is made of cadmium yellow, it is practically considered the best option because it is Highly lightfast, ... without taking into account that in a relatively short time it will be chemically transformed into something else.
3) Regarding the paint manufacturers that include it in their color charts (all), no information or warning about this problem is found and they always assign it the best permanence. Yes, best lightfast, but possibly chemically unstable, reacting with the atmosphere to become a salt.
In oil paint, the oil will not completely isolate the pigment from atmospheric factors, it will be less exposed than other paints, but even so light, air and environmental humidity will affect.
For some time I have adopted the Py74 as my yellow, and PY65 as its dark version.
I take this place to turn my concern, for being a serious space and with professional people who care and occupy in these issues of art materials.
Congratulations for the work you do.
PD. My native language is Spanish.