In last few days I got problems with making a good sheet of Sterling
silver. I am using Hoke torch with oxygen and propane. Casting into
4" wire/sheet combination steel mould.
Ok, so I bought my new Hoke torch, cast few ingots and they were OK.
I cast another ingot to make a sheet and it looked good. After
rolling it down to about 1mm of thickness and annealing it "bubbles"
appeared on the both sides of sheet. So I thought I have trapped some
air in silver, So I melted it and poured again. Rolling it down,
annealing and air pockets are there again! So I remelted it again -
but same thing happend. It was my scrap silver- clippings of wire and
sheet, few things with a little solder with it. So I thought that it
could be solder that doing this, because I have got some small crack
at the edges of sheet while rolling it - but they were small… So I
took some fine silver and fine copper, and made some new "clean"
alloy of sterling silver. Poured the ingot and rolled it down to 1mm
and annealed for futher rolling. And guess what? Bubbles shoed up
again! Remelted it but the same thing happend. So I went to the
computer, searched through Ganoksin forums, found few posts there but
there was nothing i already known about this poblem. So I looked up
itno the goldsmithing books that I have but again there is nothing
about how to solve my problem.
I am thinking that the torch could be the problem. Befor I got hoke
I used large air/propane torch to melt silver and never experienced
problem of air pockets. So I hooked up that torch and cast ingot of
"clean" alloy and scraps. Rolled them down but id didnt solved my
So what could it be?
When I am casting ingots I am covering entire mould with soot of
candle or from forch (setting small amount of oxygen). I also
preheat the mould with my torch befor casting - It is hot so you
would not want to touch it but they are not too hot (soot is
disappearing is mould is too hot). I also preheat my crucible before
I add my metal. Then I melt it with some borax, stirring with
graphite stick and then I pour with the edge of crucible as colse as
possible to the mouth of mould.When I pour metal is passing through
the flame so it wont soldify befor fillng the mould.
I also thought that my silver could be oxidised, so I used agrofulx
for reducing copper oxide and other importunities that could be in
my alloy. It also makes molten alloy more fluid. It also SHOULD
reduce chances of trapping air in silver.
As I already said, I amd using wire/sheet combination steel mould
and crucible made of fused coal and ceramics.
So what could couse air trapping in my silver? As I said before I
have never experienced this before getting my new torch, and when I
get it I have cast few good ingots. Could it be foo fast/slow
pouring? pouring from wrong side? I think not because I always have
good pouring and I dont think it have changed in one day.
Pleas give me some adivce.