Finishing Silver Castings

Q: What steps should I take in order to get a good polish on sterling silver castings?

A: For rough cutting, (assuming you’ve already emeried or otherwise cleaned up the casting) you can use bobbing compound (real fast), brown Tripoli (almost as fast), which leaves a slightly higher pre-polish surface, or white diamond Tripoli. The latter allows greater precision. I prefer it for custom work, but for production work it is a bit slower. Use any of these on whatever buff you prefer. I like the treated stitched yellow ones. Soft to medium felt wheels will cut very fast, if your surfaces can be reached with such a buff.

Obviously, for fine, sharp lapping, the harder grades of felt lap—or better yet—a split-lap wheel on an appropriate machine, is the choice. Some people like bristle brushes (which are usually charged with bobbing compound or brown Tripoli) for coarse cut-down. For final finishing, the usual choice is red rouge on a soft muslin wheel, either stitched or not, as is your preference. I like the lead centered unstitched ones. Red rouge with silver gives the very highest polish. However, it is very important with red rouge to take pains to keep the wheels from becoming contaminated with coarser compounds, or you’ll get faint scratches instead of your dead-sharp polish.

The rouge just doesn’t actually cut enough to eliminate such scratches well, as the wheel puts them in, if you’ve gotten grit or coarser compound traces on it. That means you need to clean the coarse compounds off the piece before final buffing, and storing the rouge wheels in a plastic bag between uses. If all that seems too much of a pain, you can use some of the slightly faster-cutting types of rouge. Yellow rouge is very good on silver, and gives almost as high a polish as the red. “Zam” (green rouge) is another good performer. Both of these are a little better at dealing with slight contamination on the wheel or carry-over of coarser compounds.

There is an expensive orange platinum rouge, (basically an alumina polish) made in Germany and sold by Gesswein, which is also good at giving a very high shine while not allowing a slightly contaminated buff to scratch the piece. But this stuff is costly, so I don’t suggest you go buy some just for silver. If you’ve already got some around, and find your red rouge wheel is leaving a haze of fine scratches, a little of this may help to improve matters. A better plan, though, is to avoid such contamination in the first place by thoroughly cleaning the work between polishing steps.

Silver, in general, is a little difficult to polish really well. You must be careful to keep the piece moving, in the sense that the direction of the polishing action must be sweeping across the piece and changing constantly, in order to avoid “drag lines”. Much more than gold, it can tend to show these drag marks if you’re not careful, or if the metal isn’t perfect, which is the case with many castings. And then, when you’ve got the thing finally perfect, if you leave it in an ultrasonic cleaner for too long, cast metal will often give you frosted “etch marks” or streaks, as the powerful ultrasonic waves seek out imperfections in the surface, and attack them preferentially.

Barring that, even once you’ve got it all perfect and cleaned, you have created a surface that cannot be touched by human hands without destroying the polish instantly. It looks great for show, but is not very useful, due to silver’s softness. For this reason, much commercial silver isn’t actually polished out to its maximum, but is only well tumbled in steel shot, with perhaps a quick “fluff” buffing, or is left with a white diamond Tripoli finish, which is still a pretty attractive shine, without the real high “color”. That sort of surface will show fingerprints and faint scratches less.

Larger items like hollowware are often not actually polished, but are instead “scratch brushed” with a wet, lubricated, nickel—silver wire brush. This leaves the so-called “butler’s” finish, which is durable and attractive. It’s a burnished and bright look, with faint but bright scratch marks showing uniformly all over. That same wet brass or nickel-silver scratch brush is also a great way to finish out the black antiquing you achieve with liver of sulfur, if you’re doing that. This converts the dead dull black to a shiny metallic gunmetal blue/black color that lasts much better.

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