DSS-A.03.01 — Mirror Edge Blackening (back-coating corrosion)

Localized darkening/blackening that initiates at the perimeter of a silvered mirror and advances inward beneath the protective paint (back-coating). The phenomenon results from moisture/chemical ingress at edges or penetrations, leading to corrosion of the reflective metal layer. Appearance is behind the glass substrate (back side), not on the exposed viewing face. Classification/acceptance pertain to the exposed surface only under the VIS; back-side deterioration is handled by location/scope rules.

• Perimeter “creep” band that is dark, brown-green, or black, often irregular or “map-edged,” growing inward from edges, cutouts, or scratched back-paint.
• Under-glass look: no change with front-face cleaning/reveal; no tactile relief on the viewing face.
• May be asymmetric (more severe at wet corners, splash zones, sinks).
• May show haloing around penetrations (mounts, clips) or at unsealed edges.

Surface-catch class (MSRT):

• On the exposed viewing face, record SC-0 (no relief). Perform one light, non-marring pass only; MSRT supports classification and must not abrade the surface. On suspected coated faces (front-surface functional coat over mirror glass), prefer a polymer stylus or rely on visual/location cues.

Reveal / lighting / geometry:

• Evaluate clean & dry after a Non-Invasive Reveal; use raking light and assess at 12 / 36 / 72 in at normal incidence and through an oblique sweep ~60°-120°. The back-side defect will not change with reveal and will remain visible by parallax/location cueing.

Location/access:

• Confirm the observation sits behind the glass (back-coating) rather than on the worked surface. Acceptance pertains only to the exposed surface under evaluation. Record pane ID and, where helpful, fixture/location context on Forms:

• CAT-5 (Out of Scope for In-Place Restoration): If the cue is confirmed as back-coating corrosion (behind the glass), classify CAT-5 by location/condition and refer to replacement or mirror-fabrication remedies per project protocol. Surface catch on the viewing face is non-determinative; location controls.
• If any additional face-side damage (scratches, pits, coating anomalies) is present on the exposed surface, classify that face-side condition separately under the appropriate M/Co/Ch family by CAT; do not let the back-side condition drive face-side acceptance.

Not applicable-deterioration occurs behind the viewing surface within the reflective/paint system. On the viewing face: SC-0 is expected; numeric depth for the back-side condition is not used for VIS classification/acceptance, which remain appearance-based on the exposed surface.

• vs. Front-face residues/films (R-series): Residues change with reveal and may show front-face MSRT cues; mirror blackening does not respond to reveal and remains under-glass.
• vs. Coating anomalies on the worked surface (Co-series): Coating rub/sheens occur on the exposed face and are disallowed at acceptance on coated surfaces; mirror edge blackening is behind the glass and is handled as CAT-5 location.
• vs. IGU between-pane defects: Fixed parallax within an IGU cavity indicates between-pane location; treat as CAT-5 similarly (out of in-place scope).

• Photo set (VIS):
• 12 / 36 / 72 in; normal + oblique; include raking frames.
• One edge context frame showing the advancing black band from the perimeter or cutout; one macro confirming the cue sits behind the glass (unchanged by reveal; SC-0 on face).
• MSRT result: Record SC-0 on the viewing face; one pass only; prefer polymer stylus if a front functional coat is suspected.
• Forms: Pane ID; location; reveal status; lighting/time; geometry checklist; note “back-coating corrosion (behind glass)”; attach photos.

• Attempting to “polish out” what is actually behind the glass can create needless face-side worked regions with transition edges, which VIS disallows at acceptance. Keep classification appearance-only for the face unless genuine face-side damage exists.

• A.03.01 - Mirror Edge Blackening (back-coating corrosion): “Dark/black under-glass band originating at the perimeter/cutout consistent with back-coating corrosion. Non-responsive to Non-Invasive Reveal; MSRT on viewing face = SC-0. Location/condition places the cue behind the exposed surface; classified CAT-5 (out of in-place scope) per VIS. No additional face-side damage observed at acceptance geometry (12/36/72 in; normal + oblique; raking light).”