Antique Mirror Identification: Glass, Silvering and Frame Honesty

Mirrors are two-part objects — plate and frame — each datable, often married. The plate's evidence:

Reading the glass

• Waviness and thinness: early plates (blown/broad glass, pre-~1840s) show gentle waves and imperfections — view a reflection at an angle and watch it swim; plates are thin and often bevel-less or hand-beveled (irregular, shallow bevels vs machine uniformity).
• The coin/pencil depth test: touch a point to the surface — the gap to its reflection shows plate thickness; very thin = older plate (era-consistent, not proof).
• Mercury vs silver nitrate: pre-~1860s mirrors used mercury-tin amalgam — aged ones show a distinctive crystalline sparkle in raking light and characteristic edge deterioration (fine gray-black "foxing" creeping inward); silvered mirrors (1860s+) tarnish in brown-black blotches and clouds. That sparkling decay is prized — it is the antique.
• Modern replacement: perfect brilliance in an old frame is honest and common — priced as frame-plus-new-glass.

The re-silvering question

Re-silvering an early plate destroys the mercury evidence and the original-surface premium — collectors prefer honest foxing to restored brilliance on important mirrors (the restraint doctrine); household mirrors can do as they please. Backboards matter: original old backboards (hand-sawn, oxidized, old nails) protect and prove; fresh plywood invites questions about everything in front of it.

Frame-and-plate coherence

Frames follow frame-dating rules — gilt and gesso, construction, style eras. Then the marriage audit: does plate age match frame age? Old frame + old-but-wrong-size plate (shimmed, trimmed) tells a story; so do fresh cuts in old rabbets. Married pieces are normal commerce, disclosed.

Forms worth knowing

Georgian fret-cut and gilt pier mirrors, Federal convex 'bullseyes' with eagles (heavily reproduced — repro checks on carving crispness and modern hardware), overmantels, Victorian hall trees, and venetian etched-glass mirrors (glass-on-glass construction, its own damage lexicon). Value follows frame quality + plate originality + scale; convex eagles and fine gilt work bring the premiums, assisted by the empty-frame market's logic.

Workflow

Photograph the reflection at an angle (waviness), edge deterioration macro, backboard, and frame corners (guide); the Antique Identifier app reads plate era and frame style together; comps by form and originality.

The bottom line

Wavy, thin, sparkling-and-foxed = period plate; brilliant and flat = replacement; and the backboard referees the marriage. Let old mirrors keep their gray — that's what buyers are paying for.

Values mentioned in this guide are indicative ranges from public auction and marketplace results; condition, provenance and market timing move them substantially. For insurance or estate purposes, get a written appraisal from a certified appraiser.