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A water-containing, silica-rich altered layer that can remain after more soluble glass constituents are removed or reorganized near the surface.
GlassRenu · Educational illustration
Meaning and boundaries
It is not a deposited coating of ordinary silica and cannot be identified reliably from a cloudy or iridescent appearance alone.
Why it matters in glass restoration
An altered layer can change refractive index, wetting, roughness, and polishing response, helping explain why some apparent stains are not removable deposits.
Related terms
References
- Canadian Conservation Institute — Care of Ceramics and Glass
Publisher’s original source - Canadian Conservation Institute — Caring for ceramic and glass objects
Publisher’s original source - Getty Conservation Institute — Twentieth-Century Building Materials: History and Conservation
Publisher’s original source