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Glass Inspection guide
Common Defects Inspection Criteria For All Glass Types:
- Glass must be in a vertical position perpendicular to the surface it is resting on.
- Observer must be positioned perpendicular to the glass being inspected (see example below).
- Observation must occur with the naked eye representing 20/20 vision.
- Lighting source must be daylight level with no direct sunlight or backlighting that simulates direct
sunlight.
Specific Criteria for Various Glass Types:
Flat Glass
Point Blemish – Point blemishes include crush, knots, dirt, stones, gaseous inclusions, and other
similar imperfections.
Point blemish inspection should be observed from 39” and the following are the allowable tolerances:
Linear Blemish – Linear blemishes include scratches1, rubs1, digs1, and other similar imperfections Linear.
Blemishes should be observed from 130” and the following are the allowable tolerances:
Laminated Glass
Laminated Glass blemishes should be observed in accordance with C1036 (see above).
Laminated Glass bow should be measured by placing glass in a free-standing vertical position with the
longest edge resting on blocks at the quarter points. A straight edge should be placed on the concave
surface parallel to and within 1” of the edge. The following are the allowable bow tolerances:
Heat Strengthened and Fully Tempered Flat Glass
Heat Strengthened glass may exhibit strain patterns when observed through polarized lighting conditions
and is a result of the tempering process thus not a defect.
Heat Strengthened Glass blemishes should be inspected in accordance with C1036 (see above).
Heat Strengthened Glass Bow should be measured by placing the glass in a freestanding vertical position
resting on Blocks at the quarter points. With the glass in this position place a straight edge or a taught
string across the concave surface parallel to and within 1” of the glass edge stretching from one edge to
the other and measure the maximum deviation with a measuring device. The following are the allowable
bow tolerances for Heat Strengthened and Fully Tempered glass:
Terms and Definitions
Crush – Pitted condition with a dull appearance.
Dig – A deep scratch in the glass surface.
Dirt – Small particles of foreign matter embedded in the surface of flat glass.
Gaseous Inclusion – Round or elongated bubble in the glass.
Knot – Inhomogeneity in the form of a vitreous lump.
Rub – Abrasion of a glass surface producing a frosted appearance.
Scratch – An abrasion on the glass surface in the form of a curved line, a straight line, or both.
Stone – Crystalline inclusion in the glass.
