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Casting and firescale


#1

Hi All,

I have noticed when working at the bench cleaning up casts that
sterling silver rings often have a line of firescale inside the
shank, usually in about the same place. It is at the bottom of the
shank, runs from halfway up one side to halfway up the other and
usually is centred, not quite touching either edge. I am wondering
if this is common in all workshops and why it forms in this
particular place? Most are sprued in the centre on the bottom of
the shank and I am wondering if this may be a contributing factor…

I read in an article about casting that de-oxidising agents may be
used in metal alloys for casting. I am wondering, firstly, what
constitutes a de-oxidising agent, and what effect it has. I
remember an older jeweller friend telling me about a book he’d had
when he worked in Poland (where he was born) that recommended an
additive to the alloy of only a very small amount that prevented
firestain from forming - would it have been a de-oxidising agent
that he was talking about?

Lastly, I am curious about what occurs inside of the flask during
in-stone-casting. I know that it is similar to normal casting but I
can’t see how the stones would remain in place after the wax has
been removed. Do the stones adhere to the investment?

Thanks in advance for all responses :slight_smile: