A few years ago I did a blog about the technical side of paint colors.
Today I thought I'd give a refresher. Recently I wanted to compare a couple of yellows so that I could use the one I already had.
The painting exercise called for a palette using aureolin yellow, which I didn't have. What I did have was cadmium yellow medium, and I wondered if I could substitute. Of course, in actuality I knew I could use any yellow I wanted, but would cad yellow medium be close enough to the desired palette color?
I remembered that technical information about the paint pigment is listed on the label of the paint tube or jar usually in very small type. There will be a pigment number listed if the paint is professional grade or even a better student grade; however, some student grade paint doesn't give a pigment number, just the name of the color (e.g. azo yellow light).
The pigment number is the one that starts with a P (for pigment, duh). That's followed by either a Y, R, B, Bk, Br, W, G, O, or V (for Yellow, Red, Blue, Black, Brown, White, Green, Orange, or Violet). That is followed by a number corresponding to a particular hue on the Color Index, which was assigned by the Society of Dyers and Colourists and the Association of Textile Chemists and Colorists.
Anyway, back to my problem.
I looked up the pigment number for aureolin yellow, which is PY40. Then I looked at the pigment number in very small type on my little tube of cad yellow medium. It was PY35.
Close enough for me and my paint budget. High Five!