Anybody any ideas what might work? I did read somewhere that
citric acid electro etches silver, also what about silver sulphate?
Bite the bullet and use dilute nitric. 5 percent should be enough.
alternatively, use a ferric nitrate salt in solution. the key here
is to understand that adding a battery to the etching tank does not
change the chemistry that has to occur. The electricity only
provides a substitute electromotive force for what an acid or other
chemical etchant would have done via purely chemical reaction means.
You have to provide ions in the bath that can combine with silver to
form soluable componds that exist or could form under non-electrified
conditions. Usually this means there would have been an acid with
similar ions that would etch without the electricity. Thus a
nitrate salt will, with electricity, etch silver since silver nitrate
can be formed, just as it would with nitric acid. But sulphate
salts don't work, since silver sulphate doesn't form in sulphuric
acid (if it did, then sulphuric acid pickle would etch the silver
instead of just cleaning off oxides, and we know from long experience
that sulphuric acid doesn't much etch silver. A chloride doesn't
work either, since though silver chloride forms with HCL acid, it's
not water soluable, so your electrified etching tank does the same
thing hydrochloric acid does, which is to produce on the silver a
film of silver chloride, at which point the action stops.
Normally, the two agents used for electroetching silver are either
any cyanide solution, or a nitrate containing solution, either
dulute actual nitric acid, or silver nitrate, or ferrous nitrate. Of
these, cyanide is the most dangerous, though it's been reported to
give the best etch. Were it me, I'd use ferrous nitrate salt. it's
a little harder to get ahold of than nitric acid, but is a very
slightly safer chemical, and gives a slightly smoother etch. silver
nitrate also works, and is traditional in the electrochemical means
of refining silver. I'm not sure how it's etch compares with that of
ferrous nitrate. (ferrous nitrate, like nitric acid, will etch just
fine without electric current. The electric current will speed
things up considerably, however.