CarCrash, being an engraver, most of my work is putting scrolls and animals on guns. I have done flames on several 1911's though and I'm going to do some tribal tattoo type work on some knives very soon. I can't wait to some other responses to your question.
jeepjeep, here is a shot of one of the flame guns. The slide was polished to a mirror finish, the outline of the flames cut and the are masked off. The rest was then bead blasted and blued. The flames wrap over the top and onto the other side. I was gunsmithing at the time so there was a ton of other work done as well.