Okay, here’s the thing. We are having an interesting problem at work
that we can not agree on, which has brought about an interesting
solution that we also can not agree on. I feel confident that some
wise Orchidians can explain the science behind what is happening.
The problem: We have a cast charm that is eventually attatched to a
chain bracelet. Sometimes the castings come through nearly perfect.
Sometimes they come out of casting with a terrible amount of
firescale (cloudy purplish haze in parts of the casting, or purplish
freckles everywhere). The firescale is definitely happening in
casting as the piece is never torch soldered. To make things worse,
this is never a surface firescale; it runs through the body of the
piece. Our customer requires the highest standards, and we must
reject all pieces with visible flaws, so this problem is a giant
pain in the neck.
The solution: Before the castings are polished and prepared, we send
them through our soldering / annealing oven. This oven has an
internal atmosphere that is oxygen free and runs approx 1505
farenheit. I think the heat of the oven is doing something chemically
to the cupric oxide (firescale) like removing oxygen(?). The
castings come out of the oven with a popcorn-like surface of fine
silver (?) where stuff has pushed out of the surface of the casting.
Once the pieces are polished, not all of them are perfect, but they
are much much much better, and a higher percentage of them are just
So what exactly is happening in the oven? What science is behind this
solution? I want to fully understand why this is working. None of us
here can agree.
Furthermore, how on earth does one produce a casting that is full of
firescale, when the casting is done in an oxygen-free chamber? One of
our team members has been experimenting with the quench times of the
flasks, but I dont think that can do anything to improve the
firescale. Im sure it can affect the hardness of the metal, but the
damage of the firescale is already done well before the
I cant wait to hear from you guys!