DSS-Th.03.03 — Local Heat Source Imprint (heaters / IR)

A local heat source imprint is a localized appearance change or crack initiation caused by near-field radiant or convective heating focused on the glass (e.g., space heaters, heat lamps, IR emitters, sun-facing radiant panels). It may present as a tonal/shine shift band or patch, a hot-spot nucleus, or-at higher severities-thermal stress cracking emanating from the heated locus. Classification is appearance-only per VIS (method-agnostic); any confirmed crack is an integrity condition and out of in-place scope (CAT-5). Inspect after Non-Invasive Reveal under VIS lighting/geometry; record surface numbering and worked-surface status on Forms:

• Compact patch or band coincident with the heater footprint, bracket, grille pattern, or lamp geometry; edges are usually soft (no worked transition ring).
• Gloss/contrast shift in specular view; at higher energy, modeled micro-texture may appear within the footprint.
• In severe cases, a crack nucleus forms at or near the hot spot and propagates toward an edge/corner or penetration.
• Context often shows adjacent heater placement, decals/films that focus heat, or furniture blocking airflow.

Surface-catch class (MSRT)

• SC-0 for optical-only tonal/shine shifts with no relief.
• SC-1 for very shallow modeled micro-texture within the hot footprint; SC-2 is uncommon but possible with pronounced softening.
• Perform one light, non-marring pass; do not stylus across a suspected crack. Prefer polymer stylus on suspected coated faces. MSRT supports classification, not acceptance.

Visual signature

• Local, non-directional patch or band aligned with a known heat source; no chip flanks or discrete pits typical of hot-particle damage.
• If cracking is present: phase-stable, continuous fissure(s) radiating from the hot locus (see CAT mapping).

Viewing / lighting

• Evaluate clean & dry at 12 / 36 / 72 in, normal incidence plus oblique sweep (~60°-120°) with raking light to reveal any micro-texture. Document distances/angles in-frame.

Location / access

• Record pane ID and surface numbering (#1-#4; laminate-internal). If parallax indicates a between-pane presentation, classify CAT-5 by location (out of in-place scope) and refer.

Mechanism cue (context)

• Proximity/aiming of space heaters, heat lamps, IR panels, blackout drape edges, opaque films/decals, or adjacent radiant elements; note shadow lines or reflector geometries.

Assign CAT by appearance + MSRT + morphology (three-part cueing). Depth/relief ranges are indicative-measurement is not required.

• CAT-1 (Benign / non-relief): Sheen/tone shift only; SC-0; visible mainly in raking at close/standard view. Indicative relief: ~0-10 μm (optical).
• CAT-2 (Light): Subtle modeled micro-texture within the footprint; SC-1; limited impact at standard view; no chip flanks. Indicative relief: ~10-40 μm.
• CAT-3 (Moderate): Clear detect (SC-2) with visible modeled micro-texture at standard view; boundaries remain soft; no discrete pits. Indicative relief: ~40-120 μm.
• CAT-4 (Severe): Pronounced matte/frosted hot-spot or band due to softening/devitrification; distinct at standard & wide-field views; still no peppering. Indicative relief: ~120-300 μm+.
• CAT-5 (by condition/location): Any confirmed crack emanating from the hot locus, pane instability, or between-pane/inaccessible by parallax → CAT-5 (non-repairable/out of in-place scope).

CAT is appearance-based; acceptance is separate under VIS-A at 12/36/72 in. Do not “probe” with MSRT.

• vs. Torch proximity streak (Th.02.01): Torch streaks are elongated along a tool path; heater imprints are localized to a fixture footprint or radiant pattern.
• vs. Overheated grinder/belt burn (Th.02.02): Burn lines follow tool travel and may show rubber/compound smear; heater imprints align with stationary radiant geometry.
• vs. Hot-particle damage (Th.01.xx): Slag/sparks present discrete nodules/pits with bright rims; heater imprints are continuous patches/bands without discrete pepper.
• vs. Residue films (R-family): Films remove at reveal and read SC-0; a persisting core patch/band with SC-1/SC-2 indicates thermal imprint.
• vs. Coating anomalies (Co-family): Coating rub/patchiness lacks a heater context; on a worked coated surface any anomaly remains disallowed at acceptance (VIS §6.2.e).

• Photo set (VIS): 12 / 36 / 72 in, normal + oblique, include raking macros of the footprint; add context frames showing the heater/IR source, mounting position, and distance/aim. Record distance/angle in-frame.
• MSRT result: Record SC class (SC-0/1/2) with one light, non-marring pass (polymer stylus on suspected coated faces). Do not pass across any crack.
• Forms: Pane ID; product family & surface numbering; worked surface Y/N; functional coating present on worked surface? (Y/N/Unknown); reveal status; lighting/time; geometry checklist; photos attached.
• Acceptance split: Post-restoration acceptance per VIS-A §6; classification ≠ acceptance. Coating-side anomalies on the worked surface remain disqualifying.

• Th.03.03 Local Heat Source Imprint (heaters/IR) - Localized radiant hot-spot band/patch on surface #___ with [SC-0/SC-1/SC-2]; no discrete pits or chip flanks; visible at [12/36/72 in] under VIS geometry after Non-Invasive Reveal. Context shows [heater/IR panel/film edge/reflector] near locus. Classification: CAT-[1/2/3/4] by cues; CAT-5 if crack present, pane instability, or between-pane by parallax. Forms + photo set attached; acceptance per VIS-A §6.