Can you comment on the effect of melting the same metal multiple
times and whether that too adds to the problems, especially for
The issue with reusing previously cast silver is that sulfides build
up. The rule is that you use 50% new metal, but I have reused sprues
and cast scrap without adding any new metal. I have done it hundreds
of times. Use flux and mix the metal well, but do not over flux or
the flux will run into the flask and leave voids. There is a telltale
red where the void is after the piece is pickled.
I use a centrifugal casting machine. After the metal is melted, I
add the flux, I release the pin, and I gently shake the crucible and
heat the metal making sure the sides of the crucible get hot enough
to pull the flux off of the silver. If the flame is too close to the
metal you will see black swirling on top of the metal, pull the flame
back until you see the impurities on the top roll off and the metal is
bright and shiny and then let it go.
I had a large stock of parts and pieces I had cast over time
intending to use at some point, when the economy got bad, I started
melting these pieces and I have not had any problems.
The main problem I have had with using all scrap is occasional crack
across a shank. I have not had issues with porosity. I cast hundreds
of pieces at a time and I might have a few pieces that have problems
from one casting.
Richard Hart G.G.