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Preparing for pewter casting


#1

hello all,

im interested in casting a few items in pewter, i have never worked
with pewter, gold silver inside and out but not pewter, could anyone
give me a few pointers? should i make an original the same as i would
for a silver casting to be molded? and could anyone recomend a caster
for pewter? should i use a seperate set of tools?

any help would be appreciated
heather


#2

hey there!

you can make the model exactly like you would for gold or silver.
they will then make a mold for your piece, but the mold is a bit
different for white metals like pewter than it is for regular
jewelry. but…that is not your issue.

if you are only making the model and don’t have to do any clean up
on your pewter castings, you do not need a different set of tools.
however, if you have some clean up on your pewter castings such as
filing or sanding, i would get a new file just for this and i would
work in a different area than you normally would. if you plan on
doing any polishing, buy a new wheel just for this. at least clean
your work area thoroughly before and after working with the pewter.
pewter filings can cause pits in silver or gold later on.

i do not have a good caster for you, but hopefully someone will!

joanna gollberg


#3

Heather, pewter is really easy to cast. You’ve got several options
on how to do it.

First, if you’re most comfortable with the usual silver casting
methods, you can use the same ones for casting pewter. The mold temp
for casting, after burnout of the wax, should be all the way down to
room temp. Just make sure it’s warm enough so there won’t be any
possibility of condensation (water) in the mold.

Pewter can also be nicely cast in ordinary plaster of paris molds,
instead of more costly casting investment. However, you cannot burn a
wax model out of plaster, so this is then limited to two part molds
made from a model you’d then remove manually, much like one might
make an old style sand casting mold, or the plaster molds the ceramics
folks use for slip casting… Sand casting, by the way, also works
great. So, in fact do molds made even of things like plywood, if you
are making a shape you’ll be doing some cleanup on, like handles for
a coffee pot or something. The plywood will char slightly, but that
won’t hurt anything for one or two casts.

If you make an original wax or metal model, and then make a silicone
rubber mold (not natural rubber, has to be the silicone rubbers), you
can actually cast your pewter directly into the rubber mold, letting
you do multiple castings with just the one mold, same as you’d
normally do to create wax models. The mold is at room temperature
when poured, and you can melt the pewter literally just in a tin can
over the stove (make sure it’s not a can that will come apart when
heated, and use a steel one, not an aluminum one…) I’ve done this
with standard shape/type rubber molds just as gravity pours (works,
be sure to powder the mold so air can get out, and tie the mold shut
with binding wire, or make some sort of frame, or support it in sand
or something, so you’ve got hands free for pouring. I got better,
more consistant results by making the original molds from pourable
RTV rubber, poured into a standard steel casting flask as the mold
frame (I’d cut a flask in half, so I could then extract the mold
after it had set up. It’s a harder shape to cut, but then you can
place the mold after cutting back into such a flask, put it in a
casting centrifuge, and cast it the same as you’d do with silver.
never a partial fill that way. Be sure to use a seperate crucible
for melting. If you’re centrifuge casting, let the machine spin down
totally on itself. Don’t slow it down or stop it. Pewter’s low
melting point means the cooling rate after casting, especially in a
good insulator like a rubber mold, is pretty slow, so the metal will
remain molten a lot longer in the mold than silver or gold would
before solidifying. If you stop the machine rotation too quickly, you
might find metal running back out of the mold… How long it takes
depends on how thick the thing is, but it can easily take a couple
minutes to solidify fully. The main advantage to using a centrifuge,
by the way, is that then you can get away with using smaller and/or
fewer sprues than might be needed for a purely gravity pour. The slow
cooling rate also allows you to get complete fills with less spruing
than you’d need with silver or gold

Any time you’re working in a metal with a melting point wildly
different from the metals you normally use (pewter or lead based
alloys melt far below silver or gold alloys, for example, just as
silver and gold alloys melt far below platinum alloys), then there is
a risk in using your usual tools for working with the low melting
metal. If you work with pewter and then filings or tiny scraps or
bits of the pewter get on your silver or gold alloys when you’re
working them, especially if you then heat them to anneal or solder,
then the traces of pewter can melt their way deep into the higher
melting metal, causing a deep and difficult to remove scar, or even a
hole all the way through. It’s a mess. So it’s best to not only use
different tools, but work on a different bench as well. However, most
of us don’t have that luxury, at least not for the seperate bench. So
then be sure to pay particular attention to keeping the pewter
filings and scraps cleaned up, so they won’t later contaminate your
precious metals. This is especially true for soldering blocks and
tools, and for files, which are especially good at trapping tiny bits
of metal that might then be released later where not wanted.

Peter