Gilders Paste is a wonderful little thing. I currently have a selection of four of their metallic colors. I would like to have all of their colors, but cannot find the rationalization for such a thing on my budget right now. Something to aim for! It is a type of color rub. You will see from my close ups that it is not really a full opaque coating but is more of an accent color. These comparisons were done on coral colored baked polymer clay.
I haven't found these in any bricks and mortar stores, but some internet stores will sell these. One great place to buy them is B'sue Boutiques. Her shipping is reasonable and very speedy. She also included a couple little candies in my order, their photo is not available due to reasons I don't care to mention. Ah, they were gone too soon! :-)