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Oil paint manufacturers sometimes make several "shades" of a color, all of which list the exact same chemical ingredient. For example, look at Gamblin's artist grade oils, in the yellow colors, linked here.

Two of those yellows, named Cadmium Yellow Medium, and Cadmium Yellow Deep, both list the pigment chemical as cadmium sulfide (CdS).

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If they are the same chemical, then why are they different colors? I asked the paint company and they mentioned that it is the amount of sulfide, and the temperature and amount of time in the furnace. I'm wondering, what does this translate to, in the chemistry? Are there different crystal structures to CdS? Or is the furnace introducing some impurity like oxygen? Or is it something else?

I have similar questions about the cadmium red paints that are mixes of CdS and CdSe. But the yellow is the simpler case, so I ask about that first.

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