DSS-A.03.02 — Spot Corrosion Behind Mirror (localized back-coating failure)

Discrete under-glass spots (darkening, brown/black dots, or small blooms) caused by localized corrosion of the reflective layer behind the glass where the protective back-paint/edge seal has been compromised (pinholes, scratches, clip pressure, moisture/chemical ingress). The phenomenon is behind the viewing surface (back-coating system), not on the exposed face. VIS acceptance pertains to the exposed face; back-side deterioration is handled by location/scope rules.

• Peppered spots or small clusters radiating from edge/cutout/penetration zones or at back-paint scratches.
• Often map-edged or haloed; no change after Non-Invasive Reveal of the viewing face; no tactile relief on the face.
• May progress from faint amber to opaque black with time/continued exposure.

Surface-catch class (MSRT):

• On the exposed viewing face, record SC-0 (no relief). One light, non-marring pass only to support classification; do not abrade. Prefer a polymer stylus if a face functional coat is suspected.

Reveal / lighting / geometry:

• Evaluate clean & dry after Non-Invasive Reveal; use raking light at 12 / 36 / 72 in with normal incidence + oblique sweep (~60°-120°) per VIS. Back-side spots remain unchanged by reveal.

Location / access:

• Confirm the cue sits behind the glass (back-coating). Acceptance under VIS pertains to the exposed face only; back-side corrosion is classified by location/condition. Record pane ID and fixture/location context on Forms:

• CAT-5 (Out of scope for in-place restoration): When confirmed as back-coating spot corrosion, classify CAT-5 by location/condition and refer to fabricator/replace per project protocol. Face MSRT is non-determinative; location controls.
• If separate face-side damage exists (scratches, films, coating rubs), classify that condition independently under M/Co/R families by CAT; do not let the back-side condition set face acceptance.

Not applicable to the exposed face. The deterioration occurs behind the glass within the reflective/paint system. Expect SC-0 on the face; numeric depth is not used for back-side classification.

• vs. Front-face specks/overspray (R.02/R.06): Face residues respond to Non-Invasive Reveal and may show MSRT cues; back-side spots do not.
• vs. Mirror edge blackening (A.03.01): Edge blackening is a perimeter creep band; A.03.02 presents as isolated spots/clusters, often at back-paint scratches or clip points. Both are CAT-5 by location.
• vs. IGU between-pane artifacts: IGU cavity features show fixed parallax between panes (#2/#3); mirror corrosion is behind the substrate. Use product context and forms to avoid cross-family mis-ID.

• Photo set (VIS): 12 / 36 / 72 in, normal + oblique, raking; include a macro showing spot edges/under-glass character and a context frame showing proximity to edges/cutouts/clip points.
• MSRT result (face): SC-0; one pass; polymer stylus preferred if a face coat is present/suspected.
• Forms: Pane ID; location; reveal status; lighting/time; geometry checklist; note “back-coating spot corrosion (behind glass)”; attach photos.

Attempting to “polish out” a behind-glass spot creates unnecessary worked regions (visible transition edges) on the face that VIS disallows at acceptance. Keep classification appearance-only for the face unless true face-side damage is present.

• A.03.02 Spot Corrosion Behind Mirror (back-coating) - Discrete under-glass spots/cluster; unchanged after Non-Invasive Reveal; MSRT on face = SC-0. Location/condition places cue behind the exposed surface; classified CAT-5 (out of in-place scope) per VIS. Documented at 12/36/72 in with normal + oblique + raking; proximity to edge/cutout noted.