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Yellow stain on sterling castings


#1

Hi everyone,

I have been vacuum casting sterling with a torch using the
anti-firescale method, and while I no longer have any red or purple
firescale, There is a cloudy yellowish layer on the surface of my
castings. Like firescale it only shows in the proper light or at the
right angle, but it’s not as deep as typical firescale, it comes off
with rouge, but it takes a really long time and it’s quite difficult
to remove from recessed areas. Could it be a reaction with the wax
fumes from the type of wax I use for the post casting anti firescale
procedure? I usually use bits of broken wax web since that’s what I
have laying around. Thanks for your ideas.

Douglas


#2

Douglas,

I melt with an electric melt furnace. I do not get any yellow
coating. Some times the surface is a little dull.

Fire scale is forming as soon as your pour the metal. It is
imperative you place the casting flask in the reducing atmosphere as
rapidly as possible.

I use wax filings for the reducing atmosphere. I find wax filings
produce a better reducing atmosphere. The smaller the particles of
wax the better.

Do you get the yellow layer all the time?

Normally you do not need to pickle your casting after quenching if
you use the anti fire scale vacuum casting process. However have you
tried to remove the layer by pickling? A brief time in a pickle pot
might remove the yellow. You might try coating the piece with anti
fire scale flux heat it up to the solder temp and then quench.

I don’t believe the wax is causing the yellowish layer on your
casting.

Lee Epperson


#3

Thanks for the advice Lee, I melt w/ a torch, so maybe I’m getting
firescale in the melt and not after casting. I’m going to try rio’s
anti-firescale sterling this weekend with and without the
post-casting wax treatment and see what happens.

D.