Tumble Finishing Cast Pieces

Here is my second question…

I have recently had some pieces cast for me for the first time. They
are coming to me unfinished and I am soldering findings onto them.
They have grey blotches (I apologize for sounding stupid, I think
it’s it’s firescale but I’ve never run into it before). Any
recommendations for how I can remove the grey, possibily involving
my vibratory tumbler?

Many, many thanks!
Susan Lee-Pullen

Hi Susan, My sympathies. Firescale is the scourge of anyone working
with sterling silver. Firescale can be removed by reverse plating
the items containing the firescale. The best bet to remove
firescale is to abrade it off. This assumes that the design will
allow extensive polishing with Tripoli. There is a method of
producing a thin layer of fine silver on the project by heating and
quenching. I am not familiar with the details of this process but a
search through the archives will give you the basics. Firescale forms
on sterling when copper in the metal forms with oxygen when the
metal is heated above 1000 degrees. The longer the metal is held
above 1000 degrees the deeper the firescale will be. Firescale is
worse on castings because the metal is heated to melt temperature
then allowed to cool over a long period of time. The best way to
solve the firescale problem is to never allow it to form. There are
fluxes on the market that can be used to prevent firescale when
soldering. I have developed a way to greatly reduce firescale when
vacuum casting. Have you caster contact me if he vacuum casts and I
will send him a paper on the method. The is very simple and gives
castings free of firescale. Good Luck Lee

Hello Susan, You should check with your caster about the grey
blotches. If you are not satisfied with the response, give Daniel
Grandi (RaceCar Jewelry) a call. He contributes to this forum. My
personal experience with his castings is excellent. Even though the
castings came completely finished, I’ve soldered on them with no
problems. I understand that he uses the deox sterling, so that may
be the difference. No connection, just a satisfied customer. Judy in

Judy M. Willingham, R.S.
Biological and Agricultural Engineering
237 Seaton Hall
Kansas State University
Manhattan KS 66506
(785) 532-2936