Beautiful pieces! I love them! You guys are super talented, keep it up!
Supposedly the voltage doesn't matter much (in all the tutorials it says to turn the voltage to the maximum, I don't know why, that just seems to burn the pieces). Then again all the solutions have different voltage requirements (one copper solution I have says 4V the other 0.5-1 V max) It's only the current that matters (the amps) and that should be 0.1 amp per square inch.
I've been leaving the pieces in for about 12h.
I'm going to try with a new bit, where I smoothed out the surface as much as possible, even ground down the corners and edges before I applied the paint. Will see if that makes a difference.
Meanwhile I took the piece I was working on and smoothed it with my dremel. You can see where the grooves are and how deep they go, I would have to take most of the copper off to make an even surface.
It seems like in your pieces the edge is also nice and sort of flowy, as if the copper was poured onto the piece.. mine just comes out all jagged and some bumpy protrusions break off.
As you can see it's quite thick, maybe I'm overdoing it, but that's how I imagined it's supposed to be..