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Using platinum for the first time


#1

I have a very simple cross pendant design that is two crosses sawed
out of sterling sheet, rivitted together and wire-brush finished.

I have a customer who might want this design in white gold, or
possibly platinum. Before I offer these options, I’d like to know if
I’d be getting in over my head.

I have never worked in either, but am most concerned about the
platinum.

I’ve been searching the archives for a while now, but don’t find
exactly the info I’m looking for:

  • Can I saw platinum like sterling?
  • Do I need to be extra carful of the dust?
  • Can I use the same sawblade I use on sterling?
  • How do I figure out which guage to use – as I’ve at least learned
    that platinum is far heavier and more dense than other metals.

Thanks for any help!
Jocelyn Broyles
Designer/President
www.jocelynbroyles.com
Costa Rica ph(011 506) 376.6417
U.S. fax (253) 669.1679


#2

If you have little or no experience in working with platinum, I
would recommend that you suggest white gold or palladium white gold
to your customer.

While you could probably figure out the techniques you would need to
fabricate a piece in platinum it would be a lot easier to make it in
white gold.

The difficulties you will run into with platinum are as follows:

Platinum is much heavier, and costlier than silver which means that
you need to be very careful about how you price your piece in order
to cover the material costs including waste.

Welding platinum can be done with a standard jewelers torch and a
pair of protective welding glasses. but you have to be very careful
not to contaminate your metal especially with steel, for example
Tweezers or soldering picks.

you also need to make sure that the soldering platform that you use
is very clean and can withstand very high temperatures.

Finishing platinum can be very frustrating because normal finishing
compounds and techniques may not give you the results that you are
trying to achieve. Ideally platinum needs to be sanded to almost a
final finish using progressively finer grits of finishing paper and
then finished with compounds designed especially for platinum alloys.
To avoid contamination you should have sanding and polishing paper
and wheels that are reserved for finishing only your platinum pieces.

If you have the option of using white gold this would probably be
your best bet, but you will still need to be careful not to
contaminate the material with the tools you use to do your silver
work.

Good Luck to you
Ted Curtis


#3

Well, Jocelyn, I hope you are sitting down as you read this. Since I
didn’t want to use imaginary numbers, I got a piece of 18 ga. silver
sheet, 1 3/4" x 1 1/4" - about the weight of 2 crosses saw pierced, I
think.

That piece weighed 9.6 pennyweights (1 troy oz. = 20 pennyweights or
Dwt.). Silver spot on Friday was $7.19, dividing by 20 is $.44/dwt.

Multiply by the weight of 9.6 and we get a cost of $4.22.

Spot gold was $420.90 - call it 421.

Doing the same thing, converting to 14kt. (spot x .585), we get
$12.30/dwt.

You can estimate the weight of a piece in different metals by the
ratio of their specific gravities, so 14k will weight 1.276 heavier
than silver, making 9.6 dwts. into 12.24 dwts. 14k for the same
piece. So, 12.24 dwt. times $12.30 =$150.55 for that same piece of
sheet metal.

Now the sitting down part - If that sheet is platinum, it will weigh
almost exactly twice as much, spot is $879, and there is no 14kt.
platinum, it’s just spot. So: 9.6 dwt. x 2 = 19.2 dwt. $879/oz.
/20 = $45/dwt. 19.2 dwt. x $45 = $864, just for that piece of sheet
metal.

Lest you think there is some flaw in my calculations, let me assure
you that there is not - bearing in mind that it’s only an estimate.

If anything it will probably be more. If you clipped off a wooden
matchhead, and turned it into platinum, it would be worth about $20.
Each stroke of a sawblade is worth a quarter.

I do not mean to put you off - just be aware of the realities.
Then, that piece of sheet is only one cross, my thinking being that
the scrap could be recycled into the second cross. OK, the melting
point of silver is 1760 deg. F. The melting point of iron is 2802
deg. F, and most steels run 300 - 500 deg hotter. The melting point
of platinum is 3224, but since you will be using 10% iridium plat.
(Iridium = 4449 deg. F), it will be more like 3800 deg.

And, like all metals, you need to superheat it (“till the surface is
swimming”). You need a porcelain crucible, good goggles, and you
essentially have a miniature Sun glowing on your workbench. I think
of silver, gold, copper, brass and bronze as being cousins - anybody
who can work one can work the others with a minimal learning curve.

Platinum is not the same - Yes, you use the same tools, but in
different ways. I quit using a fine file, because it loads up and
puts gouges in the finish. I use a roughing file, and then sand it
from there - very different from silver.

However, and the point of this letter - if you are reasonably
skilled, with perhaps a little coaching, you probably could do a fair
job with the craftsman part of it. It is the realities of the metals
market that many people haven’t seen yet.


#4
 The melting point of platinum is 3224, but since you will be using
10% iridium plat. (Iridium  4449 deg. F), it will be more like 3800
deg.  

Look it up again, John. 10 % iridium platinum is only a little
hotter to melt. Something like 3265, I think.

Peter


#5

Someone sent a reply about platinum saying that 3800F. was too high,
so, since I didn’t actually look up the number (the point isn’t that
it’s 326.899667 deg., the point is that it’s DAMN HOT). Johnson
Matthey shows the MP of pure plat. (all converted from deg.C.) as
3216F, that of 10%iridPlat. as 3260-3272F. The high no. is
liquidus. However, that is not the point. If one is remelting
platinum into a useful shape, you must superheat it, which is
essentially what casting does - the temperature is about the same for
a good melt. JM recommends 3632F. (2000C) for a small casting,
and 3992F. (2200C.) for large.


#6

Hi Orchid,

I hope this helps:

10% Iridium/Platinum melts at 3235 F, Flows at 3270 F, cast it at
3395-3545 F. Your flask should be at 1600-1700 F.

You might find this chart useful:
http://www.hooverandstrong.com/mill/castinggrain.htm

Eugene C. Gentile (Gino)
National Accounts Manager
Hoover & Strong, Inc.
295 Princeton-Hightstown Road
Unit 11-364
West Windsor, NJ 08550
877-687-7770
Fax: 609-936-1838
EGentile@hooverandstrong.com
www.hooverandstrong.com


#7
   Someone sent a reply about platinum saying that 3800F. was too
high, so, since I didn't actually look up the number (the point
isn't that it's 326.899667 deg., the point is that it's DAMN HOT).
Johnson Matthey shows the MP of pure plat. (all converted from
deg.C.) as 3216F, that of 10%iridPlat. as 3260-3272F.  The high no.
is liquidus. However, that is not the point.  If one is remelting
platinum into a useful shape, you must superheat it, which is
essentially what casting does - the temperature is about the same
for a good melt.  JM recommends 3632F. (2000C) for a small casting,
and 3992F. (2200C.) for large. 

for actual casting/pouring, you are entirely right. it must be
superheated. But i must comment that most of the time, in making
"ingots" to roll out, I don’t ever need to do that. Much of the time,
the whole mass of metal is not entirely melted all at the same time.
It’s for me almost like welding bits together. Sounds odd, I know.
But i pile all the scraps and bits to be melted either into a groove,
about a 3/8 inch deep and wide, and perhaps an inch and a half long.
Then with the appropriate nice hot oxidiing flame with just my normal
bench torch (the largest tip on a Hoke piece of crap torch), using
natural gas and propane, and start blasting that pile of metal.
Working from one end to the other, I get the whole top surface nicely
melted and run together, but not all at the same time, usually. Then
pick it up with carbide tweezers while still hot, flip it over, and
the bottom will generally still be recogniziable scrap bits only
partially fused together. Repeat the melting process. The result is
a slightly wider than thick bar. I sit this on one edge, and melt
that edge down into the bar a bit, flip and repeat. The result after
these four melting operations, which usually takes a couple minutes
at most, is a nice square cross section bar ready for the wire
rolling mill. Sheet metal is easier. round bottom of a wesgo
crucible. Same deal. melt as best as i can, flip it over and melt
over the probably rough and perhaps not completely fused surface, to
get a lenticular shape that’s nice and smooth on both sides. Forge if
needed to thin it a bit before rolling.

yeah, this sounds like cowboy yahoo workmanship, and I’ll be the
first to claim it would never work reliably with our other normal gold
and silver alloys, at least not to produce a good rollable ingot.
But with 10 percent iridium, this works just fine. Been doing it this
way for about 20 years with nary a problem. Solves the whole issue of
what sort of ingot mold is safe to pour platinum into, much less how
to do it without burning the place down. With just that Hoke torch,
I can easily get one ounce “ingots” this way. if I need larger,
then I have to actually get up off my duff and walk over to the
casting torch. With that, and a larger groove in the wesgo block, I
can make considerably larger ingots if i need. That doesn’t happen
often, though. Either way, I’m not really needing to fully melt the
whole mass of metal all at the same time, and no great degree of
superheat is used.

Peter Rowe


#8

10% Iridium/Platinum melts at 3235 F, Flows at 3270 F, cast it at
3395-3545 F. Your flask should be at 1600-1700 F.

1600-1700 F for a flask temperature?!?! Just curious but what
is H&S reject percentage on platinum??


#9

Peter,

Actually, I melt small “pinch ingots” of gold–yellow, rose and
white, silver, bronze, etc. in very much this manner. The metal is
usually melted through and through although I often go back and
re-fuse a section that might be finned or, after rolling, cracked.

After the metal is in a molten ball, I pinch it lightly with my
tweezers and then shape it into a nice even loaf with my flame --non
oxidizing since this is not platinum. It is ready, after defluxing,
if need be, for the wire or flat mill, depending on what I need. I
create all my bezel, wire, etc,. Like this. I can greatly extend
the use of scrap metal.

Andy