Working With Platinum

Q: I want to make some jewelry out of platinum. I’ve never tried working with it before. Is there anything special I need to do?

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.

To work with platinum, the following rules and observations may be of help: As you might already know, carbon contaminates platinum easily, causing brittleness. An oxy-acetylene torch will cause problems due to its dirty flame. 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.

Use an ultrasonic or steam cleaner on all parts immediately before any soldering or annealing, to be sure they are clean and free of any grease or fingerprints, etc, which can be a source of carbon upon heating. 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.

If you are holding the piece(s) using steel tweezers, be sure that they are well away from the areas you are actually heating. If the steel gets anywhere near the platinum soldering or fusing temps, it can contaminate the platinum. It’s possible to use such tools, but you must be careful. Fortunately, platinum doesn’t transmit heat well from one section to another, so if your flame isn’t larger than needed, and is pointed away from the tweezers, you can avoid problems. Tungsten carbide makes a wonderful burnisher, which will more easily polish small details than any other tool, and won’t contaminate the platinum. A thin carbide rod makes a safe soldering poker for platinum as well. Pure tungsten is the only other metal you can make a really safe soldering poker with. Titanium won’t contaminate the platinum, but at those temps, it burns. Steel will contaminate the platinum badly. 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.

Use either a Wesgo type soldering block (or one of their round melting crucibles, turned upside down, which is much cheaper than the actual blocks) or get one of Rio Grande’s platinum soldering blocks, which are much cheaper. They are in essence a high temp fine-grained fire brick, and softer than the fused silica Wesgo blocks, but work very well and for much less money. Forget the various other fused silica “high temp” soldering blocks others carry. Most of the ones I’ve tried are jokes. They seem to be too highly sintered, and transmit way too much heat. Soldering on one set on your bench pin quickly sets the pin on fire. And the idiots who designed at least one of the available blocks saw fit to glue on nice looking rubber feet to the underside. Guess what happens to those rubber feet the first time even a little heat hits the top of that block? Remember the line in Star Wars, where Luke, Chewy, Han, and the princess jump into a trash dump and the princess accuses Luke of discovering a wonderful new smell? Get the picture?

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. Small ingots can be cast by melting platinum into an appropriately carved depression in the Wesgo or Rio soldering blocks. For wire, carve a groove in the bottom of a platinum crucible, or use the groove in the back edge of a standard Wesgo casting crucible. Wear a dust mask, and use a Mizzy wheel or a diamond grinding wheel to carve the depression. Don’t try to cast one with a standard ingot mold; the iron will trash the platinum. Usually, you’re only making a big enough ingot for a small section of stock anyway, so this is an easy and convenient, if less elegant-looking, way to do it. You’ll find as well that the stuff rolls out so beautifully that you can successfully convert even rather rough and ugly lumps into good quality sheet and wire, where gold or silver in those shapes would often crack up before the rolls trued up the lumps. You may find when you melt the platinum onto that depression on the block that the block is melting as well, and the platinum will seem firmly fused to the block as it cools. Not to worry. Just let it cool all the way, and by the time it’s cold, it will have sprung loose again from the silica, due to differing thermal contraction rates. 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 serviceable. If you need to make long pieces of wire, roll several of these blobs out partially, then weld them 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.

Get a pair of good cobalt blue glasses for melting or soldering platinum. Rio sells em for a whopping 40 bucks, but if you call the Fend-all company, 5 E. College Drive, Arlington Heights, IL 60004, at (847) 577-7400 (I think that’s it, or get the number from directory assistance), you can get the name of a local distributor of their safety glasses. Fend-all makes the glasses Rio sells, but doesn’t sell direct. The last pair I got from their distributor here charged me $28 a pair. The same company also makes a wonderful didymium-lensed safety glass. Unlike the intensely dark blue cobalt, good for very high temps, the didymium lens is only a very light blue color, and changes your working view very little. But it almost completely blocks a very narrow band in the yellow, right where the sodium line is, which means that the bright yellow flare you get when a flame hits fluxes or glass containing sodium (borax, etc.) is completely blocked. Ordinary glowing yellow from heat is still visible, but your metal isn’t obscured by the yellow coloration the flame gets from hitting sodium-containing materials. Glass workers routinely use these glasses, and I’ve found them very useful for many delicate soldering or gold and silver melting operations where a true dark glass isn’t really required. They cost more than the cobalt, like closer to $35 or $40, but are, in my opinion, very well worth the cost. Once you try them, you’ll wonder how you managed without…

Work tight. Use as little solder as needed to do the job. Platinum solder is not actually made with platinum usually, but is an alloy of palladium and silver, except for the highest melting grades. So it’s no surprise that it’s slightly grayer and softer than platinum itself. If you use too much instead of getting seams tight in the first place, you’ll see the lines and color difference after polishing. For initial seams, especially in larger chunks, like the seam in a plain band, you can simply weld the stuff, with no solder at all. Cut the seam with a side cutter or file a notch, so it’s not a seam, but a V—shaped groove, Place a chunk of extra platinum on top, and heat just that chunk. It will heat and melt before the rest, and slump in quite nicely. Just pull back before you then melt the rest of the piece. Now forge it out a bit and file to shape, and voila—a seamless joint.

For a neater seam, say in an already made engagement ring’s shank, which you’re sizing, don’t make it such a wide V, just a slightly sloppy seam. Roll out a very thin piece of platinum sheet, a little bigger than the seam, insert it, so it sticks out about a mm. in all directions. Concentrate your sharp hissing flame just on that little insert until it fuses into the rest of the shank. Practice this on scrap stock before doing it for real, to get the feel of it. You may have to fuse first one side, then the other. Just make sure that your fusion is going all the way through the seam, rather than lingering at the outer surface. The big advantage to all this is that then you have no solder seam to “pull out” in polishing, or to be weaker than the rest of the shank. Of course, you cannot do this right next to diamonds. But you certainly can do it to the shank bottom, on a ring with diamonds at the top. With care, the top of the ring won’t exceed the temperatures that are safe for diamonds. (And as always, be sure that the diamonds are not treated or otherwise at risk from normal heating, or heat-sink the stones before doing this.)

Depending on the alloy of gold you’re using, and the design of the piece, some gold inlays don’t have to be soldered to the platinum. Instead, heat up the platinum till the gold melts into it, just like solder would have. The platinum won’t melt. Then file off the excess gold. You can use Batterns or other fluxes to help hold solder paillons in place while soldering, but it isn’t needed. However, when soldering-in or fusing-in gold inlay, flux is needed to protect the gold. High karat fairly soft gold (like 18 or 22K) alloys work better in two tone designs than lower karat golds. Platinum and gold have different rates of thermal expansion, and harder gold alloys, especially if soldered to the platinum with softer less strong solders, may tend to crack away again on cooling, or later, as the differing rates of thermal expansion/contraction create stresses in the joint. The softer, high karat golds will simply stretch or compress to accomodate the platinum’s dimensions.

Polish any platinum parts and findings and elements of the design before you assemble them. Heating won’t damage the bright polish, so soldering doesn’t disturb the polish except where the solder has flowed. This means under galleries and the like will need little work to finish up after assembly if you’re careful. And given the greater difficulty of polishing platinum in any case, anything you can do to make that job easier is worth doing. Properly emerying out a surface to fairly fine grades of emery, like 400 or 600 or finer, will greatly speed and improve the polishing process. 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 stop-gap fixit technique will save your butt on a job or two.

My favorite platinum polishing compounds are the aluminum oxide compounds from Gesswein. You use their 800 grit the same as you’d use tripoli for gold or silver, then the 1200 or 1500 as a pre-polish, and then either their 8000 as a final polish, or their “carrot” compound which leaves a slightly darker, higher colored polish. These compounds have the advantage of being hard enough to cut platinum fairly quickly, so it’s possible to minimize undercutting of solders or gold inlays, if you’ve carefully pre-finished the surfaces with very fine emery paper first. A drawback is that these compounds are quite a bit more costly than most polishing compounds we normally use. For just plain polishing of platinum without inlays or solders to undercut, you’ll find ordinary bobbing compound, especially on a brush, to be useful and fairly fast-cutting.

And last, though I’ve said it already, work clean and carefully. Many problems people have with platinum come from trying shortcuts or being sloppy with seams, cleanliness or other parts of the process. The metal is capable of many things you cannot hope to do in other metals, but it is also less forgiving of carelessness.

by Peter W. Rowe M.F.A., G.G.