Q: Some of my brass jewelry has crevices and depressions that are impossible to reach with any brushes or buffs I’ve tried. How can I polish down into these areas?
A: If you happen to know someone in the jewelry business, a caster or manufacturer maybe, who happens to have one of the magnetic tumblers that have been out for a few years now, they run not the normal steel shot, but very thin, tiny needle-like steel rods, about ¼ inch long and usually, either .3 or .5 mm thick. Those rapidly swirling needles will generally do a nice job of burnishing almost any little cavities reasonably bright, though not to a high polish. The effect is usually quite enough. But the tumblers aren’t cheap. They start, last I checked, at over $1500 for a small one. And as I said, it’s a bright finish, but not a polished one. John Patrick, who now and again contributes here, suggested a while back that his old trick, that of using carpet tacks in place of standard tumbling media, would also be pretty good at reaching very recessed and difficult to finish areas. John would pretreat the tacks (which have the advantage of costing a good deal less per pound that standard steel shot) by tumbling them with very fine abrasive/polishing compound until the tacks themselves were bright and smooth enough to burnish instead of tearing the jewelry. I think he also said he ran them with not just water and soap, but with some polishing compound as well, perhaps cerium oxide or the like. These could run in either a rotary or vibratory tumbler. If you’re doing your jewelry on a regular basis, this might be worth looking into.
On a more traditional note, the standard small vibratory tumblers, which can start for under a hundred dollars (and which are often not powerful enough to run steel shot) can be used with finely ground walnut shells or corncob media. These are usually particles about a half mm. in size and up. The commonly available versions impregnate these compounds with rouge or other similar polishing compounds. If you are starting with dull but properly smooth metal, which does not require any material removal (sanding) then these media are capable of giving you a decent low polish. You use them dry, so the mass is quite light enough for even the smallest vibratory tumblers. The rouge versions are fairly slow, but they work.
In another variation, people have also used the untreated types of this media and then added their own polishing compounds to it. One company used to market diamond compound impregnated media of this sort, which could also do light sanding as well as final finishing of almost anything, from stone to metal. Somewhat more costly media, but long lasting.
Another completely different approach which will give you an attractive final finish, but not quite a polish, is bead blasting. This is like sand blasting, but uses fine-mesh glass beads, and this stuff will reach almost anything you can see to aim the beads at. The finish is a smooth, bright, matte finish, very uniform, and quite pretty. For a dull matte finish which is also attractive, you use an abrasive medium. (Don’t use plain sand. The silica dust generated is dangerous) Some of the coarser abrasive media will actually give you a slightly sparkly surface if you like. You do, of course, need some sort of sand blaster. You can get small hand-held versions that look like an air brush, but for larger work or larger quantities, the best is an actual blasting cabinet. Costs start a bit over a hundred for very small simple ones; a decent one goes for much more. You can also get rather crude hardware store blasters, at a cost of somewhere around 20 dollars or so. Harbor Freight, or other import/discount tool suppliers, and automotive tool suppliers often have them. These are just the blast guns, hoses with a pistol grip gun, and no cabinet at all, so you end up losing your media and making a mess. And they need a lot of air, so you need a fairly large compressor (forget about the air-brush compressor from the art store). But for a one-shot deal, you can get something to work for you. It is possible to improvise your own cabinet from a cardboard box with cutouts. For compressed air, you can get air tanks that you fill at the gas station if you don’t want to buy a compressor, but don’t count on blasting for a very long time between refills.
If you were working with gold or silver, I’d suggest electropolishing, which is the reverse of electroplating, and can brighten recessed areas nicely. But the solutions I’ve seen don’t work well on brass. It might be worth some phone calls, though. Just because I haven’t seen them doesn’t mean they don’t exist. There are low-tech solutions you could try. Small rotary brushes in a flex shaft or Dremel, like larger brushes on a polishing machine, still need room to rotate. The end brush styles can get into a lot, but even so, often it’s hard to reach true blind recesses, corners, or square-bottomed areas. But a hand held brass bristle brush, not having to rotate, can often be scrubbed down into very small areas. Use a very soft fine bristle brush, and lubricate it with soapy water, and you can often bring up a nice smooth bright satin finish on brass that’s very pretty—not a high polish, but attractive. The best brushes I’ve found for this are called plater’s brushes. Dixon makes them, they have wooden handles, and cost about 7 or 8 bucks.
Also, you might give a glass-bristle brush. a try. These are marketed often with the watchmaking tools, but work nicely on brass and gold as well, leaving a smooth matte finish. Lubricate them, and the finish is a bright matte. They usually look like some sort of drafting tool, an automatic pencil sort of thing, with a¼ inch round glass fiber brush end that can be extended out of the housing as needed. It’s a useful little tool to have around.
Now some other ideas…If you can find a tool of the right shape to get into your low spots, such as a used-up burr or cutter, then you can take that tool, smooth off the sharp edges with Tripoli, buff it to a highly polished but now bumpy (from what’s left of the teeth on the cutter after buffing) tip, and go over the cut surface. Use a little lubrication here and a slow speed. You’re now “power burnishing”. The result will not be perfect, but can improve areas you just cannot otherwise reach. Even a jeweler’s sawblade can be converted this way from a cutting to a polishing tool, (though not a great one). In a similar vein, round wood toothpicks can be chucked into a flex shaft and run with your choice of compound. Same thing with cotton swabs (Q-tips), where the cotton can be stretched out into a long point to reach areas an end bristle brush doesn’t quite handle. The q-tips don’t last very long, of course, but who cares?
And for cutouts and openings, if you can thread a piece of string into an opening, you can polish it very nicely. The string will hold buffing and polishing compounds as well as any buff. This goes fast and works well. Finally, if in polishing some of these small details, you find that your original surface is wavy, and after polishing its lack of smoothness makes it look bad, go get a couple small “scotch stones”. These are small rods of a slate-like stone, available in a variety of sizes from about 1/8 inch to ½ inch square and around 4 inches long or so. You grind the end to a shape that can reach the area you’re working with, and using it wet, manually lap it down. This may sound slow to those who’ve gotten too used to power tools, but the stones will cut about as fast as a fine file, and can be whatever shape you want, (it wears down quickly to conform to the surface you’re stoning), and leaves a very fine, smooth, stoned surface, about equivalent to a 400 or 600 grit sandpaper surface, that’s easily buffed up to a higher shine without distorting the now smoothed surface. These things are really wonderful for detail finishing in corners, or things like stoning off a little excess solder in an area you cannot otherwise reach without distorting a surface.
by Peter W. Rowe M.F.A., G.G.