I have just started forging silver and have probably overworked the
silver. I tried carefully heating the silver with an oxy-acetylene
torch to fuse the cracks together without melting the whole piece. I
succeeded in not melting the bar, but there appeared little holes in
one area. Anyone with have any idea what the origin of these might be
an ingot from scrap silver that I have been accumulating for awhile.
TIA
Stephen
but there appeared little holes in one area. Anyone with have any idea what the origin of these might be from my description?
You probably had defects in your original cast bar. Little bubbles
of trapped impurities or oxides or even air, or small shrinkage
cracks/voids… Things like that. When you then heat it with the
torch, some of these will burst just like bubbles. They may also be
the underlying reason why you got cracks in those areas in the first
place.
Silver, for what it’s worth, is sometimes harder to get a good ingot
or bar with than it seems. Rolling good sheet metal from a cast
ingot, for example, is something I find a lot harder to get with
sterling silver than with, say, yellow golds. Very often, by the time
I get the sheet rolled down to a reasonable thickness, when I then
anneal it, I get some blisters showing up as bulges in the sheet.
These are areas where absorbed gas pockets, or other impurities,
which spread out during rolling, expand on heating. Annoying. When I
make sterling sheet metal, I just assume I’m going to get some bad
areas in the sheet, and plan on needing to work around them. Wire is
a bit easier to make, since those same types of defects when rolled
and drawn to wire, don’t end up as spread out blisters, but rather
threadlike long inclusions, generally down the middle of the wire.
That can still cause problems if it’s more than minor, but often the
wire is still usable.
The fix is that you’re ingot or bar pouring routine needs to be a
rigorous as possible in eliminating causes of these defects. Melting
furnaces seem to work better than torch melting, at least for me, and
the temperature of the ingot mold is important too, to get proper
progressive solidification of the bar without forming shrinkage gaps
in the center. If the metal you use has been used several times
already, then steps to deoxidize it are useful. Proper fluxing of the
melt, or addition of deoxidizing agents like a little phos-copper
can help too. But even with your best efforts, you’ll likely still
get occasional defects.
Peter Rowe
the holes you mention are probably from boiling the silver.
solution? use argentuium sterling. melts, fuses like gold zev ps
with all fusing be gentle with flame, no boiling try to stay near
fusing temp
the holes you mention are probably from boiling the silver.
Very unlikely that he is boiling the silver, silver’s boiling point
is 4013.6 F and copper’s is 4652.6 F way beyond the melting point of
most crucibles FWIW
The bubbles are most likely oxygen as silver is an oxygen sponge
when molten.
James Binnion
James Binnion Metal Arts
But even with your best efforts, you'll likely still get occasional defects.
Oh boy, not to reopen old subjects (well why not, given other recent
re-openings) but sometimes its better to buy milled stock. Yes,
sometimes you want something milled your way but if the result is
uncertainty in the material one must ask,“is it worth it?” You could
also buy milled product, then mill yourself from there, that way you
know the metal itself is sound. Particularly if the offending defect
doesn’t show up til you’ve committed significant resources. Because
then you have to ask yourself do you run with it and hope no one
notices, or do you start all over again? If you’re in business for
the long run, I think there’s only one answer.
So personally, I’ll just take the safe, cost effective in the end,
way. Its not a philosophical question, its a practical one. But to
each his own, for his own reasons. A larger production shop would
hopefully have worked out processes to the point of a very low
defect rate, and their volume would make in house milling more $
attractive. A small shop, or a newbie…better to do what you do,
which is final product, not necessarily milled materials production.
Sorry.
Silver can dissolve large volumes of oxygen. when the metal cools
and solidifies this gas comes roaring out!
Any bubbles left in your work will cause porosity. This occurs in
other metals too but silver is exceptional. You can reduce this
porosity with melting practices.
Melt with a reducing flame. use a flux cover. use a carbon cover,
use a carbon stir rod. An Eectromelt furnace helps a lot. These are
all very important but before you start with these Learn to design
your work and sprue system so the last metal to cool is in the
sprue.
I have cast a bunch of bronze with 50 pound pours. These are
susceptible to gas porosity too.
With carefully planned sprue design I can recover as 40 pounds in a
sculpture. Don’t ignore this engineering! silver is only worse but is
manageable.
Seeing a hollow sprue after a cast makes me happy-- I know it is not
in the product.
jesse
James,
The bubbles are most likely oxygen as silver is an oxygen sponge when molten.
How does Argentium Silver compare to sterling in this regard? I just
rolled out my first Argentium (970) ingot and haven’t seen any
problems. I used a pinch of boric acid, even though I’ve read some
places that it’s unnecessary when casting AS. Did I get lucky or is
AS better suited for rolling than sterling? Also, is boric acid
necessary or unnecessary?
Thanks,
Jamie
How does Argentium Silver compare to sterling in this regard? I just rolled out my first Argentium (970) ingot and haven't seen any problems. I used a pinch of boric acid, even though I've read some places that it's unnecessary when casting AS. Did I get lucky or is AS better suited for rolling than sterling? Also, is boric acid necessary or unnecessary?
Argentium is just like plain sterling in that it is at least 92.5%
silver and silver is the bad actor here. Silver holds huge amounts
of oxygen in its molten state,22 times its volume is one reported
number (1cc silver 22cc oxygen!). So you need to be very good with
your melting practice when working with molten silver. Maybe you were
lucky maybe you haven’t found the gas yet, sometimes it hides till
you have invested many hours in something just to show up as fine gas
porosity in finished surfaces 
Fluxes like boric acid help a little but not nearly enough to
overcome bad practice. Talk to any refiner who actually produces
silver sheet stock (some don’t they just buy from others who do)
they will tell you what a pain in the butt sterling production is.
Most have gone to continuous casting machines to make sterling
because they can control the atmosphere much better in those machines
than in open melting furnaces.
James Binnion
James Binnion Metal Arts