RE: [Demo notebook] Reference notebook: corrections and recurring beginner questions · RWI-21920

Case 39 — Crystal reflections: why a dark patch is not a coating test · source wording exercise

Summary draft for “Crystal reflections: why a dark patch is not a coating test”: the answer addresses “Compare multiple controlled angles and describe the visible observation without asserting…”; the related point is “No single lighting setup settles…”. Keep both connected to the opening question, and mark any conclusion needing further records as unresolved. Review focus: source wording. Retain the source wording beside any paraphrase.