Button and casting scrap re-use

[note: this was posted to RCJ but due to moderator lag exceeding 24 hours I
decided to post here]
Eager newbie "silversmith" (term used very loosely) back with another naive
question begging to be skewered or helped.... =)
I start out with verified sterling or .999 and take care to prevent
contamination during casting. When complete I have at least a button left
over and sometimes a partial cast for the scrap pile due to incomplete
burnout, poor spruing and the like. Assuming the contaminates could include
residual investment material (SatinCast) and possibly wax that didn't
completely vaporize. Shouldn't be much else, maybe some carbon from the
floaters MAPP gas sends in the air.
So the question is what processes do you guys follow to re-use the metal. I
read a book that basically says re-use it mixed with "fresh" which makes
sense when it comes to sterling, maybe not so much with pure. In sterling I
understand you lose some alloy but I wouldn't think that's as much of a
concern as outright contamination of pure silver would be.
I had a couple ounces of buttons I put in the crucible and melted down to
create shot but I wonder if there is minute particles of SatinCast or other
contaminants still in there I should be concerned about. And what
procedures you guys/gals follow.
Thanks for any pointers.
- Ben
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Contamination is only one concern. Alloyed metals experience oxidation with each heating. If you re-melt your metal too many times, it will start casting with porosity, a result of included oxides. It's best to use up your old alloyed metals as they accumulate, as suggested, by adding them to fresh metals each time you cast. You'll stay out of trouble that way.
Pure silver doesn't oxidize readily----so that's not a concern, but contamination is. Wax and satin cast won't combine with silver to change its composition, so it's not of concern. Wax would burn off harmlessly, and investment should float on top, easily skimmed. Re-melting pure silver by using clean instruments should yield clean silver------unless you contaminate the charge with metallic elements. Include only known silver bits----anything that isn't known should be refined to extract values.
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Harold and Susan Vordos

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