How to clean a dial you must not touch
An enamel dial with hairline cracks is not washed — only dusted with air.
Enamel on old dials cracks not through but in a net of fine lines. Dust gets into those lines, and any moisture drives it deeper — after that the mark cannot be removed.
So dials in the collection are treated only with dry air at low pressure. Two of them have stayed greyish, and the collector does not try to lighten them: the grey is dust that has become part of the surface.
