\Nils Schwarz shared the best silver etching process I have used so
far. He used a solution of phosphoric acid for anodic depletion. I
tried it using Ospho from my local hardware store as the mordant with
a titanium sheet for the cathode and my antique plating rectifier as
the DC source. It worked great. There is no undercutting. The etched
lines are shaped like square bottomed V’s.
Ospho is safe, cheap and easy to get and as far as I know it isn’t
very toxic to dispose of. John Flynn