|Q: How hard is platinum to work with- should I leave it to the experts? I heard it takes a lot of heat to melt, and casting it was difficult. Is there anything I can do with it that doesn't take special equipment?
|A: It's true, perhaps, that not every jeweler has tried platinum work, and many younger workers haven't yet learned it, it doesn't require an absolute specialist either, just a well-trained reasonably experienced all-around jeweler capable of precise work. Contrary to some common myths, it's not actually all that hard to do, once you've learned how- it just needs practice.
While I'd agree that platinum melts pretty hot, the only really specialized equipment you need to work with it as a jeweler is an appropriate pair of dark glasses, and an appropriate soldering/melting block to work on. (Some experience and knowledge and practice helps a lot, though). After a while, you'll accumulate some other specialized tools. Most of 'em you'll have made yourself, and often out of nicely polished carbide. It's different to work with than gold or silver, and follows somewhat different rules which you must follow. But with practice, you'll learn to love it. It's not so forgiving of mistakes, but it will also let you do things you could never do in gold or silver.
What IS difficult to get good at with platinum is casting the stuff. Getting good castings consistently can be a real problem, even for professional casters with expensive equipment. So, send out the casting work, and get good at fabrication.
For you beginners, here's some tips to start with. The bottom of a Wesgo round fused silica crucible works well to melt in, or Rio sells a cheap firebrick type of block that also works for soldering, though less well for actual melting. They also sell a nice pair of cobalt blue glasses. Often, as with gold work, you'll need to make an ingot to roll out sheet metal or wire you don't already have, or to reuse clean bits and pieces. For wire, carve a groove in the bottom of a Wesco crucible, or use the groove in the back edge of a standard Wesgo casting crucible. Melt the pieces in that groove. The longish blob you'll get will be firmly fused to the silica when still hot, but by the time it's cooled to room temperature, it will be completely released. Turn it over, and if the other side is too rough, you can just melt that surface to smooth it.
Now, it can be rolled to the form you desire. If needed, you can hammer-forge it first into more of an ingot shape, but platinum will tolerate much more "abuse" in rolling odd shapes without cracking apart in the rolling process, so these "lumps", though not as attractive as a mold-poured ingot, are entirely servicable. If you need to make long pieces of wire, roll several of these blobs out partially, then weld 'em together to make longer pieces. And in drawing wire, if you've got a carbide drawplate, the round holes can produce a wire so perfectly polished that if you're careful, the final polish on the piece won't be able to improve on the original drawn finish which remains.
In melting and soldering platinum, the key point is to use a harsh oxidizing flame at all times, . Oxygen and natural gas or propane are fine fuels. Oxy-hydrogen is better, but not so much so that I'd recommend you go right out and get a new setup just for platinums. With a normal Meco or Hoke torch you can easily make ingots of half an ounce or so. Flux, as well as the normal boric acid firecoat, is not required. A little flux, though, can be useful to help hold paillons of solder in place. Soldering is generally done with paillons placed on the joints, instead of the common practice in gold-work of using a poker to bring solder to the joint. Getting good at this, by the way, will improve your gold soldering joints as well, since soldering gold with a poker can often lead to overheating of the solder, with resultant pitting.
The cardinal rule for working in platinum is to Keep Things Clean. You must not allow the platinum while heated to soldering or melting temperature to contact carbon ( including reducing flames, charcoal blocks, or greasy dirt burning off from heating a dirty piece), or iron, both of which can contaminate the platinum. Steel tweezers can be used if kept far away from the heated area, so as never to get hot enough to cause contamination. Especial care must be taken that filings and bits of gold or silver don't contaminate the platinum when it's heated, or they will burn into it the same way lead will burn into heated silver or gold. Wash residues off the platinum after rolling or drawing, before you anneal it, for example.
The need to keep steel away from the hot zone can make holding the workpieces difficult. Carbide-tipped tweezers, such as those available for the GRS benchmate soldering station (my own setup, as it happens- there are others as well) will prevent contamination, but are also strong heatsinks. So often, a joint must be "jigged" or otherwise planned so that it can be positioned or held together for soldering. Very often, the simple trick of leaving bits of wire long enough so you can still grab the far end with tweezers to solder the other end, instead of cutting things to length before, will do the trick. Or wires can be bent around, with one end clamped by tweezers to another part of the assembly, while the far end is soldered. (This is easier to do than to explain here.) Think of putting two prongs onto a ring, part of making a multi-prong head, for example. Instead of soldering one wire, and then the next, you fit a longer piece of wire bent into a U shape, so each arm of the U is in position to be one prong. You can clamp one intersection of one arm with the ring, thus holding the other one for soldering. After soldering both, the bottom of the U can be cut off. Get the idea? Anyway, a little preplanning as you assemble a piece will generally reveal ways of supporting and holding things while you assemble them. Platinum is a poor enough heat conductor that it is possible to space consecutive joints in a piece quite close together, without melting the previous joint, using the same grade of solder on all the joints.
Take the time to see that each component of a piece is well finished-out before you assemble the piece. Platinum is difficult enough to polish that taking the time to polish the parts of a head before you assemble it, even when you know you are likely to get some tool marks to deal with along the way, will still save you much time later.
A hint here: platinum is hard to polish, but, with a carbide burnisher, very easy to burnish to a wonderful shine. In some cases, it's much faster than normal polishing sequences, and can leave as good a finish- if not better- especially on small details and areas that are hard to reach...
The burnisher can be made from a small piece of carbide rod, ground with diamond wheels to a bullet shape or whatever you wish, and polished with lapidary diamond compounds. I refinish my carbide burnisher from time to time, when I don't wish to actually fire up the lapidary equipment, with a birch disk, about 2 mm thick, sliced from the end of a 1 inch dowel, and drilled to mount on a pinhole arbor. It's placed in the flex shaft machine and trued up, then a groove is cut into one face, which is then charged with a little diamond compound. 3,000 grit compound will smooth the carbide, 8,000 or 14,000 will polish it nicely, and a final polish with 50,000 will get it super-glossy. The result of using a truly well-polished burnisher on platinum can be truly wonderful.
Another useful carbide burnisher for dealing with less-than-perfect castings, is a variation on the common "bent burr" trick. An old bur is bent over at one end and cut off so that a little "L"- shaped end is created, maybe 1 or 2 mm offset from the shaft centerline. A little bit of carbide is brazed to that bent end, shaped to form a ball, and then highly polished. Chucked into a flex shaft, at low to medium speed, it will hammer/burnish out porosity very effectively. While a similar tool in steel is effective on gold, it tends to drag too much on the platinum. The carbide does not, burnishing properly. That carbide tool is pretty nice on the problem areas in a gold casting too. A note on using these tools: as you rotary-burnish over an area of porosity, it will look like you're creating a rather bumpy surface. Some of this is just the hammering action, but some is because you're compressing sub-surface areas of porosity, causing slight dips in the surface. Work the surface thoroughly this way, then lightly sand smooth again, not cutting so deep as to go through the lowest spots, which were your worst areas of porosity. Obviously, it is much, much better to have a casting which is not porous in the first place, thus not needing this rather abusive finishing technique. But it's not a perfect world, and casters aren't perfect either. So there may be times when this stopgap fixit technique will save your butt on a job or two...