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White metal (spelter) and pewter casting sculptures


#1
I was looking at art deco sculpture photos and came across some
really neat Irenee Rochard's beauties. I read the descriptions and
many of them are cast in white metal being described as spelter.
What exactly did they cast these in? Some descriptions say it has
zinc others just say it's basic pewter. 

There’s no precise definition for “spelter”; it’s applied to any
"white metal"or"pot metal" containing zinc. They can also contain
copper and/or lead and tin.

I am curious because I would like to cast some of my own small
scultpures and would like to know of other choices than just
silicon bronze. 

If I understand correctly, a real pewter, if that’s what all of these
Irenee Rochard sculptures seem to be, is made of at least 94% tin.

“Pewter” is another generic name for a family of alloys, usually
containing some amount of tin. Old recipes usually had lead in them
as well, but modern alloys, like Brittania Metal, are lead-free.
There are various recipes for lead-free pewter that are basically
tin with some admixture of other metals like antimony that improve
its working properties and durability.

That's interesting that back in the 1930's or 20's using pewter
was perhaps cheaper than bronze? Because today, isn't finding pure
tin very difficult to create alloys for casting large pieces of
pewter with? Silicon is much easier to buy I think to make your own
silicon bronze, plus you only need a little of silicon and mostly
copper for the bronze. 

Most foundries buy their silicon bronze and pewter pre-alloyed, but
I suppose you could mix these things up yourself. It’s generally
cheaper and easier to get these things in ingot form, though, than
trying to source and deal with the pure metals. I don’t think tin
was ever cheaper than copper. Those pieces from the 20s and 30s were
not cast in high-tin pewters but in pot metals made from copper,
zinc and lead.

But with pewter, you need a boat load of pure tin. which I thought
is near impossible for someone to purchase to make a bunch of
pewter. 

At least, this is what I gather from reading many of the home
foundry forums.

So do I understand correctly that tin used to be easier to buy for
making pewter, plus with the lower melting point, it was used for
mass producing sculptures, but today, for the home foundry artist,
the lower melting point of pewter is not a good enough incentive
for the high price and impossibility of a near pure tin casting
alloy? 

While the cost of high-tin pewter is more than the cost of bronze by
the pound, that’s not the whole cost equation. It’s a lot more
difficult to work with bronze, since the casting temperatures are
much higher. You need to either make sand molds, do ceramic shell,
or use plaster-based investments that are burned out in a kiln.
Pewter, on the other hand, can be cast directly into rubber molds or
permanent molds made of metal, ceramic or stone. So the ease of
working with it balances out the higher cost of the metal, at least
until you’re making fairly large pieces. If you don’t insist on
alloying it yourself from pure tin, it’s not hard to find; here’s a
source that sells a variety of lead-free high-tin pewters for about
$20/lb (or less if you want more of it):

http://www.ganoksin.com/gnkurl/ep81nj

For comparison, silicon bronze in small quantities goes for about
$9/lb, or $6.50/lb if you buy a whole 20 lb. ingot:

http://www.ganoksin.com/gnkurl/ep81ni

Andrew Werby
Juxtamorph.com