I'm interested in doing something similar and have just beeen searching the archives, only to find this pretty-darn-recent post.

What I want to do is transfer a carbon-gelatin image onto copper (or other metal), and then use a patina formula to get a 'patinograph'. Again though, one would need a half-tone negative to get gradations.

There appears to be some halftone screens on eBay. They are all magenta in color, and say 'magenta'. Why is this? Do they have cyan and yellow? I don't quite get why the screen itself has to be colored, as it itself is presumably not a separation filter. Or is it?

BetterSense, have you attempted anything thus far?