Monday, July 21, 2014
The acid I can buy over the counter is pretty puny stuff; it's only about 28%. I can boost its activity somewhat by adding hydrogen peroxide, but again the stuff I can buy easily is only 6%, so the added oxidizer is offset quite considerably by the fact that I'm diluting the acid with mostly water — I'd prefer using at least a 30% peroxide solution.
What that means is that etching takes a long, long time, and the shellac I was using as a resist just isn't up to the task; it started to break down after an hour or so. If you zoom in on the image, you'll be able to see where the acid crept in under the seams where two layers of shellac met.
I'll see if I can lay my hands on some proper resist lacquer, which should do a better job. I'd like to get some stronger acid too, but that's likely to be problematic.