I've been trying some things regarding this weathering of a copper hull. I've done 3 tests.
1) Using the Humbrol Chrome Oxide with a gloss verniz. The result is vissible on th etop right of the test plate I used. As you can see this is a dissaster.
2) I used the Humbrol Chrome Oxide with Decal soft from Revell so you get a wash effect. The procedure works better but it is not the right color (Chrome has a different color while oxidized as Copper so makes sense). Result is vissible on the right bottom side.
3) I took a turquoise enamel paint and applied the dry brush technique. This result is visible on the left side.
I think I will go for option 3 even though I really would like to use these powders as I have seen nice results but for this purpose I think it doesnt work. The turquoise has a much more realistic color for copper oxide.
But if anybody has other opinions or ideas feel free to give them.