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Silver contaminated in crucible


#1

Does anyone have any guesses what might have been in my crucible? I
was melting a students metal. Should have been sterling silver, but
a couple of things happened which made me doubt this alloy. First,
the melt was much brighter than normal. Almost painfully white hot.
Next, there was a slag. Not heavy, but enough to bother me. The
student told me the crucible had contained nothing but sterling
silver buttons. When I spun the arm, some of the metal flew out of
the crucible, some went in, but what was left behind was a
purplish-black coating on my crucible. Not the red-purple color, but
black. I told the student his metal must have been contaminated. But
he said it was impossible. Can I use this crucible again? It was a
new one, and I need to cast more students work.


#2

Hi Cindy,

but what was left behind was a purplish-black coating on my
crucible. Not the red-purple color, but black. I told the student
his metal must have been contaminated. But he said it was
impossible. Can I use this crucible again? It was a new one, and I
need to cast more students work. 

If it were me, I’d scrap the crucible. Since you don’t know what was
in the metal that caused the problem, using it again will probably
cause problems with any metal melted in it. It wouldn’t be a good
idea to contaminate someone else’s metal. The cost of a typical
centrifugal casting crucible is usually under $20.

Dave


#3

Wonder if any of the buttons had the little hoops some buttons have
that you run the thread through, as opposed to holes the thread runs
through? If so those probably were NOT silver. Just a thought.

Beth Wicker
Three Cats and a Dog Design Studio
http://www.bethwicker.com


http://bethwicker.ganoksin.com/blogs/


#4
If it were me, I'd scrap the crucible. Since you don't know what
was in the metal that caused the problem, using it again will
probably cause problems with any metal melted in it. It wouldn't be
a good idea to contaminate someone else's metal. The cost of a
typical centrifugal casting crucible is usually under $20. 

I clean up my crucibles with molten borax from time to time. Just
get a good melt going and pour it out. Repeat as necessary.