Vitreous enamel dials are made by fusing powdered glass to a copper or, less commonly, gold base at high temperature in multiple firings, with the numerals and any decoration applied and fired separately. Properly fired enamel is hard, glossy and resistant to fading, but it is brittle: hairline cracks, chips at the edge (especially around the winding stem hole) and star-shaped impact fractures are common and, once present, cannot be fully removed by cleaning.
Silvered dials are usually solid metal — silver, or silvered brass or bronze — with a matte, frosted or granular surface produced chemically or mechanically, over which hours, minutes and any signature are engraved, printed or applied separately. Silvering tones with age and handling; a dial resilvered to look bright and new has lost original surface, which specialists can often detect from the crispness of engraved lines and the character of the surface texture.
Painted or printed metal dials, typically brass, became common as production expanded and enamel firing costs and breakage made a cheaper alternative attractive, particularly in mass-market American and later mass-market Swiss production. Numerals and markings are printed or painted rather than fired, which makes them more vulnerable to wear, fading and moisture damage but easier and cheaper to refinish.
Refinishing is a legitimate conservation choice for a badly damaged or illegible dial, but it changes the object: original printing, original patina and original signature crispness are evidence, and their loss reduces both research and (where relevant) market value. A refinished dial should be described as such, not passed off as original.
Signatures, retailer names and grade markings on a dial are strong attribution evidence, but only when consistent with the movement: a dial that names a retailer or grade inconsistent with the movement it sits on indicates a marriage, a later replacement dial, or an aftermarket alteration, and should be recorded as an open question rather than resolved by assumption.
When cataloguing a dial, record the material if it can be determined, the type and condition of markings, any hairline cracks or chips with their location, evidence of refinishing or repainting, and whether feet and mounting match the movement without packing or filing — each is independent evidence about the object's history.