metallic inks and/or pigments

I was wondering if anyone has had any experience whatsoever with metallic inks and/or pigments which could be added to inks. I have some bromoils I want to make and use metallic inks for a glow/shimmer effect. Also pearl would be good too, but slightly different. I'm just having the worst luck here trying to find any such thing. I know it exists though! It has to! There's metallic lithographs for gosh sake! heheeh

I would like to find out where to purchase. How easy or difficult it is to work with them.