Inspection panel for oven door has sub-surface laser markings consisting of identifying numbers, letters or symbols

摘要

A glass body has an upper surface, and a lower surface with laser markings consisting of identifying numbers, letters or symbols. The laser mark extends to a predetermined depth and is focused at a point within the glass. The laser beam creates a material change which results in a visible mark on exposure to a secondary material change but without change to the glass surface. The glass surface is hardened and has areas of compression and tension.