I used copper soldered onto the corner of my sheet for the first
piece I etched, and I was not impressed. The copper, although
seemingly well masked, still gunked up my solution quickly. I think
it’s best to only use metals of the same kind – I just now leave a
"tab" of the sheet I’m etching to attach my lead to. Also, if your
alligator clip was touching the water at all, it was being etched
away, too, contaminating your solution.
I used the warm 7% salt solution for several of my first etchings. I
wasn’t that excited by the results – it didn’t etch particularly
evenly, and was leaving some areas that didn’t even have resist
unetched. We got good results with pieces that had very fine lines,
and not a lot of them. Overall, though, it was just a little too
corrosive, I think. Last night my husband and I tried warmed sodium
bisulphate (Sparex under the brand name, but waaaay more expensive
than regular ol’ sodium bisulphate), and we got really nice results.
The etch was a bit slower, but much more even and the nice thing is,
it basically pickles the work, so you don’t have a thick layer of
corrosive crud gumming up your work. The resist also doesn’t seem to
get “consumed” and undercut like it was with the salt. It is, of
course, irritating to lungs and mucous membranes, so doing this
under a hood or outside would be the most desirable.
It’s also important to keep an eye on your amperage. If you’re
pushing too much current, it can blow out your resist and just
create a mess. We have been using PnP Blue, touched up with Sharpie
in the small areas, and nail polish in the larger ones. Packing tape
or Scotch tape on the backs seems to be working just fine. A
fiberglass brush works well for removing resist. We’re still in the
learning process, but with each piece it seems to be getting better!