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Casting issues with sterling silver

I’ve read through the blogs, but haven’t come across anything like I
am seeing with my casting. I am melting and pouring clean scrap
sterling silver (it’s the first after factory melt and it’s clean of
any solder and other things) into wires and ingots in the same molds
I’ve always been using. I am following all the steps I normally take
to do a pour, but have changed one thing. Instead of covering the
cast iron mold with soot, I started using regular petroleum jelly
(unadulterated with perfumes or anything like that). What I’m finding
is that there is notable porosity in some of the rods and ingots,
approximately 1/2 of the pours are failing. One of the most
interesting things I’ve found, is that a wire that looks perfectly
poured and shaped, without any signs of porosity or blems on the
outside surface will actually have a tube like appearance when it’s
cut. I had three same sized wire ingots from the pour and noticed
that one felt lighter than the other two, curious, I sawed into it
and sure enough, I could have used it as a tube setting (with some
serious clean up with a bur of course). Has anyone experienced this
before? I remelt and pour scrap metal quite a bit without adding new
material in the past, so was quite surprised to experience this. The
weather is still quite cool here in Terrace, but the formation of the
"tube" ingot is a bit perplexing, the tube ran the whole length of
the ingot with the exception of 1.5cm approx at each end, of a 7.5cm

Thanks! Sonja

sounds like a cold mold…are you heating it well, before pouring?


Sounds like the silver is cooling too quickly in the ingot mold. Are
you pre-heating your ingot mold while you are melting your silver. I
have my ingot mold supported by two fire bricks over my melting dish
so by the time the ounce or so of silver is melted the ingot mold is
nice and hot.

Rick Copeland

go back to the soot method, the petroleum jelly is ablating and
cooling down the mold.

Mark Zirinsky

I discovered the problem with the cast. There was no problem with the
molds or the metal being too cold, just a little over zealous with
painting on the Petroleum Jelly. When I went back to try again, I
wiped off most of the jelly leaving only what was left from wiping
the mold down and the subsequent casts were perfect.

Thanks for the responses!