These paints were epoxies, or basically oil paint: pigments in simple mixtures of thinners and oils that polymerize (turn to plastic) via oxidation. In this case they were very thoroughly cured by repeated baking in the paint booth. Many of the pigments were toxic--you only need to think about lead-based paints--so I don't know how I'd feel about my wife wearing a necklace of the stuff against her skin. A ring, like the example above, is perfectly safe.
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As a follow-up to the metallurgical display case post, I've just discovered that they're making rings out of ceramic. They're not exciting structural ceramics like silicon nitride, but they're the real thing and characteristic of the breed: lightweight, hard as hell, and brittle. The ceramic used seems to be zirconium oxide, familiar to jewelers in single crystal form as fake diamonds (yttria-stabilized cubic zirconia) and to dentists as fake teeth. They're available in white, black, and a couple pastel colors. And they're cheap!