The Chemistry of Oil Painting

What chemical properties give oil paintings their luminous glow and deep darkness?

Why do they crack?

What kind of oil is used?

Is it safe to use the oil painting medium on a fresh dandelion salad?

As an oil painter for the past 17 years who used to manage at a fine art supply store and notably not a chemist, I'll do my best to explain. Don't slip on the floor, and remember to soak your cleaning rags in water before disposing of them in the metal bin. They can spontaneously combust, you see.

Introduction to what paint is and isn't

All fine art paints share a few properties that make them different from say, dyes. Paints are essentially pigment particles bound in a sticky, transparent medium, whereas dyes or soluble in the liquid. So oil paints are pigment bound in oil, acrylic paints are pigments bound in acrylic polymer medium, and watercolors are pigments bound in a water-soluble medium called gum arabic. Fabric dye and fabric paint are therefore not the same things.

There can be other agents inside a tube of paint these days, that slow down or speed up drying, that lend texture, or help stubborn pigments bind to the medium. (Inexpensive paints often have too much binder in them and can cause discoloration over time - check out this post by artist Jonathan Linton on his blog Theory and Practice for some empirical tests.) But at their root, all paints are pigment+medium.