IGMA Thermal Stress Task Group
Submitted by Steve Marino, PPG Industries
Edge Condition
Low Risk
Polished edges
Ground edges with or without any exposed shiners.
Clean Cut edges with a uniform seam using a 120 grit or finer belt or grinding wheel. The seam
is where the cut edge is ground off to an angle of approximately 45 degrees. The width of the
seam is approximately 0.8mm (0.030”).
Medium Risk
Ground edges with offset grind that is caused by improper grinding wheel set-up. One of the
original cut edges is exposed above the grind.
Clean cut edges with a uniform belt seam using 100 grit or courser belt. Deep gouges are
visible in the seam from the course belt material.
Any seamed edge over borderline cut edge
Borderline cut edges - shark teeth up to ½ glass thickness, serration hackle, and/or chips
Shark Teeth: Dagger-like imperfections which start from the score surface. The edge strength
and resulting potential for glass breakage increases as the depth, roughness, and number of
shark teeth increases.
Serration Hackle: Edge imperfections, usually perpendicular to glass surface, which occur at
surface opposite the score. The edge strength and resulting potential for glass breakage
increases as the density and depth increases.
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High Risk
Cut edges with deep serration hackle
Cut edges with deep shark teeth (>1/2 thickness)
Cut edges with serration hackle with spalls
Impact damage to any type of edge condition
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