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Purify Platinum


#1

Hi I am not into jewelry making but a friend of mine has a question.

How do you purify Platinum ? ? ( a million dollar Question but only
willing to repay in kindness ) (Smile)

Once a platinum ring is made there is platinum dust , scraping and
residue. How do i prepare this for re use. ? because when I re heat
and use , it cracks and its unusable.

Any help to solve this problem is highly appreciated.

regards
Ahmed Shareek


#2
   Once a platinum ring is made there is platinum  dust , scraping
and residue. How do i prepare this for re use. ? because when I re
heat and use , it cracks and its unusable. 

Ahmed, refining/purifying platinum is the most difficult of the
refining tasks. i’d recommend that you use a fine seive to sort all
the small scraps from the actual dust. then use a magnet to remove
iron from the larger scraps that did not go through the seive (be
careful here, since if you use cobalt/platinum alloys, they are
magnetic too, and the dust from those will be also stuck to the
magnet. All the dust is perhaps best sent to a full time refiner.
there is almost always significant amounts of iron (from file teeth,
sawblade teeth, traces from other tools), assorted abrasive dusts,
dirt, and all sorts of other junk in there. This can be difficult to
remove economically, unless you are doing larger amounts. The larger
scraps can generally be inspected to be sure they do not contain
solder, and are indeed platinum, and then usually can be directly
melted. If you are certain that the platinum dust does not
contain gold, you can dissolve it in aqua regia, just as one might do
for gold, and then precipitate it back out in similar manner. I’m a
bit rusty on the details, though. Consult a copy of Hoke’s “refining
precious metal wastes” for the full details. It CAN be done. But
it’s complex enough, with several steps, and somewhat costly
reagents, that most people feel it’s more economical to sell the
scrap to a refiner, who’s doing large enough amounts to be able to
economize.

Among other things, just refining the platinum does not return it to
either the fully pure, or the alloyed state you need, such as iridium
platinum, or ruthenium, etc. The refining process tends to not so
easily seperate the platinum group metals, so they all stay in the
final result, at least to some degree, though not always uniformly
so. This means that if you refine it yourself, your finished product
may be of indeterminate alloy, unless you are very careful with the
techniques, and follow all steps precisely. As I said, this isn’t
beginner level refining.

Hope that helps.
Peter Rowe


#3

Ahmed, Platinum is a wonderful and profitable metal to work with. It
can be melted and used over and over endlessly. The cause of the
cracking is contamination of some sort. All bits and pieces of
platinum that are free of solder and other metal can be remelted. As
can platinum bench filings produces by a saw or rotary file or any
steel tool. The trick is to make sure it is very clean. Keep a
separate pan or a baking sheet to put under your bench pin during
de-spruing and rough filing platinum pieces. Keep this material
separate and clean. Do not let it become contaminated with emery or
rubber wheel dust or you will have to have it traditionally refined.

When you are ready to remelt your platinum scrap, it must be soaked
in a heated 10% nitric acid bath for several minutes. This removes
any steel left behind from the file or saw blades. There may only be
trace amounts but, it will be enough to ruin the platinum. While it
is easy to soak the bits and pieces, filings can be a little
trickier. The filings can be placed in a sheet of platinum that has
been rolled out paper thin then folded around the metal. Close the
ends so that the filings will not come out but that the nitric acid
will still be able to get in and clean the metal. (A friend of mine
described it as similar to rolling a joint but, I’m not sure what
that means.) Remove this package from the nitric, rinse it, dry it
and melt it as one piece. This accomplishes two things. It
eliminates the need to filter the nitric to get your platinum and it
allows you to melt the filings without having the stuff blow all
over the place.

Some other things to remember are. Do not mix platinum alloys. .95
cobalt is not compatible with 10% irid ect. Melt the platinum on a
crucible made for platinum such as a Wesgo crucible. Use this
crucible for platinum only and store it in a clean place. I have
never poured my molten platinum into an ingot mold. Instead I melt
it in a groove carved into the bottom of the crucible. When rolling
platinum stock always soak it in a 10% nitric solution before
annealing. The heat it takes to anneal plat. is enough to cause
material picked up from the rolling mill to fuse into the platinum.
Platinum must be annealed. To accomplish this bring the piece to a
bright cherry glow and hold at this temperature for one minute per
millimeter of thickness of the stock.

Also, pick up the book Praktikum Platinschmieden/ Practical
Platinumsmith by Ruhle-Diebener-Verlag and any of the literature
produced by the Platinum Guild International. It will be worth your
while.

John Sholl
J.F. Sholl Fine Jewelry
Littleton, CO