I have used both and believe me, fine is the only way to go.
Pat - there are literally millions of cast and
stamped Sterling silver pieces still floating around e.g. the
Charles Horner Art Nouveau stuff - and I defy anyone to get more
reflectivity using cast 999 fine silver than the majority of those
Hundreds of thousands of Sterling compacts, pill boxes, vanity sets
picture frames etc have been made and many of them are still in
existence. Although most of them weren't cast, the principle is the
same - you are not enamelling on the Sterling alloy itself, but on a
layer of pure silver. The surface of an object made of 999 fine
silver and the surface of an adequately depletion-enriched 925 Ag or
for that matter 800 Ag object will appear IDENTICAL once they have
been heated to redness, with or without vitreous enamel covering
them. They will be a uniform, flat, no-gloss silvery-white regardless
of whether or not they were highly polished prior to firing.
If you have brought up a substantial, even layer of pure silver on
the surface of your Sterling that is what you will see through the
enamel. If there are no casting flaws e.g. pits, inclusions, etc -
and there rarely ever are if the piece is cast using the best of the
available technology by some one who actually knows what they are
doing - then you will have no problems.
Problems invariably occur when people attempt to enamel castings
they or their mates or the bloke down the road have produced. While
these might be perfectly adequate for the average bit of jewellery
nothing but the highest quality castings will survive multiple
heatings to bright redness unscathed.
Also it should be minimum of 18 ga.
Walk into any antique dealer and inspect some old
enamelled Sterling jewellery.
Yes, you can fire/pickle/fire/pickle sterling until the surface has
no copper or zinc
Sterling contains no Zinc - if there is Zinc there it ain't
left, but even then you are walking a treacherous path with the
stability of colors and transparences.
The incompatability with silver of enamels containing colloidal gold
is well-known and occurs when there is ANY amount of silver in the
surface to be enamelled - it is irrelevant whether one uses Sterling,
999 silver, or gold alloys containing silver. It is an entirely
Here are some pictures of Sterling pieces and one 18k yellow piece
I've enamelled, including two Horner brooches and the hatpin
yesterday ( hatpin is < 0.3mm thick - try making that out of 999
fine silver and expecting to use it without it folding up at the
first push) The pendants are about 0.5mm thick, the brooches, 2mm,
the frogs were new work for a Melbourne jeweller: