Workshop Hints
Swirled metal finish or 'spotting'

The British Horological Institute has archived and edited the following from e-mails sent to the Clock/Clockers mailing lists on the Internet. The information here does not necessarily indicate a method approved by the BHI, we are only publishing this digest so that others can decide for themselves whether the methods listed below will suit them.

From: Bruce A. Clemens, Dewey Clark, Alan Heldman, Bill Wilkes

The swirled metal finish popular in the 20's and 30's is called "spotting". In clocks and watches this is entirely ornamental.

It is done by mounting the workpiece in an X-Y table, and presenting the end of a rotating cylinder charged with an abrasive to the surface of the workpiece. This polisher is then lifted, the X-Y table is shifted an increment (say 1/2 the diameter of the polisher) and the polisher is again presented to the surface. After 1 row is completed, the X-Y table is adjusted to start the next row.

For Small workshops, there are several ways of getting this finish.

(1) chuck a wooden dowel in a drill press; put some water slurry of grit, or grinding paste, on the face of the piece you want to decorate; bring the turning dowel down onto the grit for a second or to, then move the work piece. If you want to get a really accurate overlapping pattern, you need to put the work piece in a compound vice or compound table where you can control the X and Y axes.

(2) same as above but less messy is to use "Cratex" pieces. It's a rubber material with abrasive build into it, throughout the body of the rubber; found in jewellery supply catalogues and such.

(3) use the erasure end of a pencil with an abrasive compound. It is a very tedious process, but does look nice.

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