Alum & jewels

[tpmcan]

Working on a nice old Hamilton pocket watch which I disassembled and cleaned yesterday. The only thing besides needing a new mainspring was that one of the little screws that holds the lower balance jewels in the plate has the head half broken off so that it can't be unscrewed. I've used alum for screws on other watches but not w/ the jewel still in. I don't think alum would hurt the jewel but does anyone know for certain? Thanks.

Tom

[Bob Tascione]

Hi Tom,
I don't think it will hurt the jewel either. Highly reactive with ferrous metals for sure but I think it's rather inert when it comes to brass and other non-ferrous metals. I've had no problems. Probably best to test it on an old jewel if you have one though just to make sure it doesn't stain it.
Sorry, not much help I know.
Take care for now,
Bob

[tpmcan]

Thanks Bob. For anyone else who's curious, I took Bob's advice. While waiting for my new mainspring to arrive I took an old cracked cap jewel in a brass setting and put it in a saturated solution of alum in warm vinegar water for 36 hours. Result- one clean cracked cap jewel. As I think about this, alum in vinegar water is your basic pickle juice. Pickle juice doesn't hurt glass jars (silica). No reason it would hurt watch jewels (silica) either. It didn't. As it turned out, I don't have the exact replacement screw for that broken one so I'm going to leave it alone, oil the thing in place and see how it runs after servicing.

Tom