For once a subject I actually have some experience with!!! :-))
Etching patterns into silver is what started me on the bumpy road of
trying to make jewellery, in an attempt to make a special present for
a girl I liked. It never worked out with the girl, but it taught me a
lot about etching! The technique I used is, however, somewhat
different from those discussed on Orchid, namely electro-etching.
I prepared the design on A4 sized transparencies and then took
photographs of the patterns on a light table. I then sprayed the piece
of silver to be etched with Kodak Positiv 20 Photo Copying Paint
(Photoresist). This was dried at 70 Degree celcius for 30 minutes. The
developed B&W negative was the applied to the coated silver as a mask,
and exposed with ultra violet light and the exposed part was dissolved
off with7g/l NaOH solution. The other masking methods described on
Orchid should work equally well.
As most of you probably know, chemical etching tends to cause
undercuts, i.e. the metal get eaten away under the edge of the coating
rather than just in the exposed areas. This becomes a real problem
with intricate designs having thin lines, that need to be etched quite
deeply. Electro-etching has quite the opposite effect. As electricity
is ‘lazy’ it tends to take the most direct route. So instead of going
around the edge of the coating it causes the etch to taper inwards
like this: _/ This results in very precise lines down to a width
of only 0.2mm. Only when the depth of the etch becomes greater than
the width of the line does under-cutting become noticable.
As an etching fluid almost any conductive liquid will do, but I found
10% phosphoric acid to be best. It is also relatively safe to work
with. In fact you could probably use Coca Cola as this contains quite
a lot of phosphoric acid ( reason why it is so ‘good’ for our teeth
I used 0.5V and 0.02A for a piece the size of a 35mm negative. The
amperage will obviously vary depending on the surface area exposed.
Most patterns etched beautifully in about two hours. I sometimes
plated copper into the etched designs afterwards, as this gives a
really great contrast. The etching solution will work equally well on
copper, but somewhat slower. Unfortunately the photoresist is attacked
by alkali plating baths, so filling the etch with gold plate requires
plating a copper strike onto the silver and then using a chloride
based gold solution.
Hope this info is of some use.
Cheers from a chilly Johannesburg