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Stains when polishing Argentium

Q. When I cast Argentium after polishing a piece, black stains appears on the surface. I can not remove it pickling or polishing.

Where is the problem?
Adriana Cuellar
AJM - Santa Cruz, Bolivia
2006

A. This looks like fire scale. Most likely your flask was too hot or your melt was too hot or both.
Neil Bell
Albuquerque, New Mexico

That is fire scale, it can be removed with aggressive polishing.
Marc Banks
Blacksmith - Elizabeth City, North Carolina

You can use a chemical solution for cleaning and Ag surface pasivation (to be maintain clean a long period!).
ALEXANDRU SAVU
SC SAVPROD SRL - Bucharest, ROMANIA

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