While out visiting designers a couple weeks ago with Duke of Reich Paper, edge painting came up. Mainly, because each time Duke gave out his card, it was met with much enthusiasm. His card is a super thick 236 lb. cover of 100% cotton, Savoy that has been letterpressed, foil stamped and edge painted in a studious, slate blue. These thicker papers are a must if you want to edge paint and really see the results. You'll want to specify and use at least a 120 cover but even thicker is better. We've got lots of choices for you.
I'm a big fan of edge painting. It gives a wonderful pop of interest and color. Edge painting is a process that can be done on just about anything - business cards, invitations and book edges. I asked Duke lots of questions about the process since his luxe paper line is commonly used for this technique. It seems that edge painting is somewhat shrouded in mystery. Each letterpress printer has a different technique for applying edge paint. Some roll, some spray, some use acrylic or dye and rub it on. Printers don't commonly share exactly how they do it. Imperative to the process is a clean, sharp guillotine cut to a stack of cards and snug clamping of the stack to be painted. Check out this informative post I found on "Oh So Beautiful Paper" to see one of these processes of edge painting.
And not only can you edge paint but you can also guild the edges with silver or gold metallic leaf for a bit of bling. The guilding is much more time consuming but the results speak for themselves. See a video of that process here with a master guilder at Crane's.