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Platinum sizing stock


#1

Hello All: I am doing more and more platinum sizing. I know we
have touched on this a couple of times but I was wondering how
one goes about making platinum sizing stock? I have never tried
to pour a platinum ingot and I don’t even think my torch would
get hot enough to melt much. Does everyone pretty much just
purchase platinum square stock and roll it out from that? I
really don’t want to buy a whole foot of 4mm X 4mm square stock.

Michael Mathews Victoria,Texas USA


#2

You need, first off, some version of a Wesco type crucible or
soldering block. the back side of one of the round melting dishes
works well, or their soldering block, or do what I do: Take
cracked and unusable casting machine crucibles, and with a
lapidary slab saw, remove a slice from the bottom, thus turning
the crucible into a soldering block…

anyway, useing a diamond grinding wheel in your flex shaft,
(Carbide works, but it will trash your carbide burr) carve a
modest sized V shaped groove in the block. I usually use one
about an inch long, and maybe 3/8 inch wide.

Place the soldering block (or upside down crucible, if that’s
what you use) on a standard soldering block, rather than directly
on your bench, as it will get hot enough on the underside to burn
your bench.

In that groove, you can place assorted scraps and bits and
pieces of platinum. Be sure they are quite clean, with no solder.
Using a Hoke Torch, or a Meco Midget, with Natural gas or
propane and oxygen, you can melt down about 3/4 ounce to maybe an
ounce or so, in that groove. Wear properly dark glasses, this is
brighter than orinary platinum soldering. You Probably won’t
get the whole mass to melt at one time if you’re doing a fairly
large amount. That’s OK. Just fuse along it from one end of the
groove to the other, and down each side, so it looks like a
continuous long blob with a fairly uniform and smooth surface.
Should be nice and bright. then let it cool. It will, while
still hot, be firmly fused to the wesco soldering block, which
partially melts during this process. but the two have different
rates of thermal expansion/contraction, and as it cools, the
platinum will break free of the block. Turn the blob over. The
bottom will look a mess, and may even have only partially melted
bits of platinum still there, or it may just have what appear to
be deep pockets and voids. Anyway, fuse up this side the same
as you did the other side. Take your time, and be sure that
you’ve welded deep enough that fusion is completely through the
blob.

The result isn’t as nicely shaped as a poured ingot. It’s just
a long blob. If you tried this in normal gold alloys, and tried
to roll it, it would crack all to hell. Platinum won’t.
Depending on your square wire mill size, vs. the size of the blob
you’ve fused up, you may need to either open up your rolls quite
a bit to get it through the first opening, or you may even need
to hammer forge it down to a size where you CAN get it into the
mill. Take great care that you don’t fold over any "wire edges"
or burrs. they won’t start cracks that would then extend as much
as they would with gold, but even so, they’ll create flaws in the
rolled ingot. Any such flaws that seem to be starting can be
filed off before continuing with the rolling. Once you’ve got it
to a point where it’s completely being formed by the rolls, you
can treat it the same as any other piece of metal you’re rolling
down in size.

The procedure is the same if you need sheet metal, except then
you start with a round depression, such as that melting dish
bottom, or a similar one you can carve in your soldering block.
You then fuse up a round flattish button, hammer it flat enough
to fit into your rolls, and roll away.

Platinum is extraordinarily malleable. You can take one of
these crudely melted pseudo ingots that starts out as a crude
blob 3/8 inch wide and a quarter inch thick, smash it through the
rolls down to a standard square wire size, and run through the
entire rolling mill sequence, ending up with the smallest size
on your square wire mill, (on mine, that’s about .9 mm, flat to
flat), without annealing even once. If you’re careful not to
create any burs that fold over, the metal will be fine. I
usually do anneal it once when the crude ingot finally is fully
squared off and even, and then again about half way through the
rolling sequence, but as much as anything, that’s habit, not
actual requirement of the metal.

Now, drawing the resulting wire round, if you need, is not quite
so forgiving, as the drawing friction of platinum is fairly high,
and it’s not quite as ductile as it is malleable. What that
means is that if you don’t anneal it often enough, you’ll be
breaking it. But it’s still more workable than most gold alloys,
being much like a standard 18K yellow gold, except a bit harder.

For many of the pieces I make in platinum, a major portion of my
work, by the way, much of the metal stock I use is made up this
way. Shank stock, sheet stock, wires, jump rings, etc. We do
buy 2 ounce ingots that come as flat square pieces about an inch
square and maybe 4 mm thick. These, I try to reserve for those
times I need larger pieces of sheet metal. The scraps from that
use, as well as sprues from castings, constitutes most of the
input of platinum to our working stock at the bench. Lots of
times, I’ll have plenty of metal, but not in the right sizes, or
it’s bits and pieces, or whatever. With platinum unlike many
gold alloys (the casting alloys, at least), if you’re careful not
to contaminate the scrap with pieces that have solder on them,
you can continue to remelt and reuse this metal almost
infinitely, with no deterioration. I’ve even, in a pinch, reused
sawdust. Don’t like to do that, but if you’re sawing thick metal
with a coarse blade, and carefully saving the dust, making sure
the bench pin was completely free of other metals (I use a
plastic tray that I place in the bench pan when I need to catch
the platinum scrap seperate from any other scrap on the bench),
then the dust will be mixed only with the occasional sawblade
broken teeth, and whatever sawing lube you used. A magnet takes
care of the sawblade teeth, and the resulting dust can be
carefully collected and remelted into useable metal. Trying to
torch melt sawdust with golds would lead to a lot of oxidation,
even with flux, but with platinum, you can do it if you’re
working clean enough, and are low enough on platinum stock in
your inventory, usually with a rush job that must go out, to
warrent going to these lengths to reclaim the scraps. The
platinum dust is dense enough that a small torch flame (still
must be oxidizing) won’t blow it all away…

Enough already!

Hope this helps.

Peter Rowe


#3

If you value your time, simply order as little as an inch from
Hoover & Strong, If, however you intend to cast in platinum, use
Stuller as their plat/cobalt will work better than H&S plat/irr.
You don’t have to buy an entire foot of 4X4.

Best wishes;

Steve Klepinger


#4

hi mike, it takes a brave and foolish sort to pour platinum
ingots in a sm studio, tho it can be done with the proper
crucible and a graphite ingot mold. it’s really tough to see
where one is going to pour that 2200 C mass of platinum with
11 specs on. being really quick with the pour is essential
as well.

one could just melt a button in the crucible and flip it over
and weld the bubbles in the button out and then roll it out into
whatever. or one could order platinum casting material in the
form of sheet cut offs (this is what i do).

best regards,

geo fox