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Investment cast and torch

I use aceylene entirely, and 80% of my business is platinum - I
have no problems related to gas 

I had to learn the hard way about Pt and Acetylene, it was all I had
when I first started and I have some scrap that is really brittle
and does not form well without breaking, but I did have some that
turned out fine and no problems, I was also using a graphite
crucible, (Big No No) but hey that is how you learn with no one to
teach you. But I found that if I used a really heavy oxidizing flame
it would turn out fine, it is a minimal amount that went bad and I
think it is because I did not to that.

That is my take on the whole Oxy/Acetylene thing, it does
contaminate, but you can get it to work too.

Aaron A Tracy


There was another very interesting comment on this thread about
silicates and carbon, too. The real point, I think, is that we live
in the real world, not a theoretical one. If one could melt platinum
in a vacuum (do-able), not touching anything else, suspended in “the
ether” (not), with electrical heat, it would be perfect every time.
But we, at the bench, need to do it for real, and the metal has to be
in, or on Something, and electrical heat is impractical at the bench.
I use a porcelain “Platinum” crucible - melt in the side-grooves to
get more of an ingot. A charcoal block will trash your metal, and
burn to a crisp, too. Oxy-Acetylene is, above all, the hottest flame
we can get, in practice, and I use all the O2 I can get without
blowing the flame out - hissing, bright blue cone. It’s fast
(because slow melting is not good for metal, either), and clean
enough for practical purposes.

A comment to students Re: Which torch? Again, distilled to the
essentials, there are only a few-acetylene/air, oxy/acet.,
air/propane, etc. Just to stress- don’t be confused by Brand-Names,
The first choice is what “Type”, and then pick a cost/handle/gas/regulator combo.