Workshop Tips

Plaster in bezels

In the July 1994 issue of the Horological Journal, Mr J K Nicholson offered this suggestion for replacing the damaged plaster found in some clock & barometer bezels.

One often comes across a clock or barometer with glass that has been cemented into a cast brass bezel with a hard white material. Often this material has deteriorated to the point where replacement is required.

I have tried using normal dental plaster. Several problems usually occurred, The extremely rapid setting coupled with the difficulty of handling the 'sloppy' plaster rendered a neat job difficult. When the material had set I was never entirely satisfied with the adhesion between the plaster and the glass.

During working in the manufacture of Spirit levels, I discovered that the tubes were secured by a paste of ordinary wheat flour and Plaster of Paris. This was mixed in equal amounts and water added in the normal way. The resulting paste was easier to handle and setting was slower with excellent adhesion between the glass and the bezel. The final hardened material was also less brittle.

After testing some original plaster from a bezel I found that there was starch in that too. It would seem therefore, that the same or a similar mixture had been used in the past.

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