Platinum Finishing Techniques
Finishing platinum is really no more difficult than finishing any other precious metal. It is, however, quite different. With a little practice and a proper understanding of the procedures and materials, a very fine finish and a histrous polish can be achieved. This will take time, effort, technique and the right polishing materials.
When we talk about the jewelry finishing and polishing process, we are discussing the reduction of scratches and the removal of small pits and other blemishes on the surface of the metal. A finish is defined as the surface treatment that will alter the appearance of a cast product. A finish is defined as the surface treatment that will alter the appearance of a cast product, with techniques such as Florentine, matte, brushed or hammered or otherwise textured in some fashion. Polishing, on the other hand, creates the mirror-like luster on the metal’s surface. Until the decision is made to either apply a mechanical finish or a high luster, all the initial steps of preparation are the same.
Platinum’s density and scratch resistance require a succession of finer and finer abrasives to reduce the scratches until they are microscopically small, thus presenting a high polish to the eye – a luster that will outlast any other shine. The surface should be mirror-like, without any blemishes or waves. There should be no visible porosity.
After the removal of the sprue or after a repair is completed, use minimum filing to create a smooth surface. Just remove the high spots with a file. Be sure the file is cutting forward strokes and is not dragging across the platinum on the return stroke. This technique will prevent smearing as well as clogging the file. If porosity is encountered, a highly polished tungsten burnisher should be used to burnish the porosity away. A small amount of lubricating oil, such as oil of wintergreen may be used to facilitate the burnishing. The burnishing will work harden the surface of the casting, this will make it somewhat easier to hold a high polish. In some cases it may be necessary actually fill porosity by fusing small amounts of metal into the affected area(s). The metal used in this operation can come from the small sprue that is removed in the early finishing.
Use progressively finer abrasives, such as silicon grade carbide or alumina papers on a sand paper stick. Grits 220, 280 and 320 are most commonly used. Unitized wheels in grits 400, 500 and 600 can be used to create even finer scratches. Sand papers are also available in those grits. As you switch from one grade to the next, sand at 90 degrees to the previous direction, removing all scratches from the previous grade. To prevent cross-contamination from gold or other metals, segregate all abrasives for platinum use only and keep them, as well as other tools in a separate location.
There are some new tools on the market where ceramic particles are bonded and mixed with a rubber carrier material. The ceramic surface is quick to cut without clogging. The different grits are quickly identified by color coding. Red and blue are coarse, #80 and #120, green and purple are medium, #220 and #320, and orange is a fine grit at #500. They are mounted on 3/32 shanks for flex shaft motors and can be run up to 30,000 rpm.
After all of the surfaces have been prepared to a uniform 600 finish, with crisp edges, the actual polishing process can begin. Using a hard felt wheel, charged with a polishing compound, a progressively finer scratch can be obtained. There are many compounds that will accomplish this job, however we recommend the compounds supplied by Gesswein. The gray 800 grit compound, followed by the white 1500 grit, then the white 8000 grit is a way to create a terrific polish on platinum. The final luster can be achieved using the carrot or orange rouge compound. It is important not to cross-contaminate individual wheels and to clean the jewelry piece prior to using the next finer compound. In other words, if a wheel is used for 8000 white compound, do not use it for any other compound or for anything other than platinum jewelry.
It is helpful to polish individual components prior to assembly, while they are easily accessible to the polishing wheel. It is especially important to pre-polish the platinum if gold pieces are to be joined to the platinum. This is because it takes more steps to polish platinum and one would tend to over-polish the gold. Because platinum does not oxidize during the fusing/welding process, the finish will not be altered at assembly. A firecoat of boric acid and denatured alcohol is recommended to protect the gold components from oxidation.
If you follow these instructions, polishing platinum will not be that complicated. All of these steps will become second nature and the results will be a luster that can only be achieved by platinum.
Make sure to check out our Jewelry Casting section for more information about our casting services. If you have any questions concerning the above suggestions, or we can help you with any piece, please contact us. We will be happy to assist you.