What are the standards for allowable visible defects in decorative architectural glass?

Glass industry standards regarding visible defects are set by ASTM International.* Understanding ASTM inspection criteria is very important, before identifying and pointing out defects and imperfections. The criteria outline inspection distance, lighting requirements, inspection times, etc. The official ASTM standards are quite long and can be difficult to follow, therefore we are providing this brief summary of the visual inspection criteria, as well as how to determine if a defect is allowable or if the glass may be rejected:

• Glass shall be inspected in the central area: in transmission at a distance of 5 feet from the observer, and in reflection at a distance of 10 ft. from the observer. Note: Bendheim’s inspection standard is always from 5 feet.
• Glass shall be inspected in the border area in transmission and reflection at a distance of 10 ft. from the observer.
• Glass must be inspected using a viewing angle of 90 degrees from the glass with suitable background light.
• Inspection should not exceed viewing of more than 5 seconds for lites up to 6 sq. ft., 10 seconds for lites up to 35 sq. ft., and 20 seconds for lites larger than 35 sq. ft., either in transmission or reflection.
• If defects are visible beyond what is allowable — as outlined in the table below — using the above inspection criteria, the glass may be subject to rejection.

 

Defect	Allowable When	Max. Allowed on Lites up to 6 Square Feet	Max. Allowed on Lites 6 to 35 Square Feet	Max. Allowed on Lites Over 35 Square Feet
Scratches*	Size is 1” or less	1	2	3
Debris, Dirt, Spots*	Size is 1/16” or less	1	2	3
Seeds, Bubbles, Knots, Stones*	Size is 1/16” or less	1	2	3
Shells	Located no more than 1/4” from the edge and less than 1/2 the thickness of the lite	1 per side	1 per side	1 per side
Chips	Located no more than 1/8” from the edge	1 per side	1 per side	1 per side

* For these visible defects: no more than 1 total defect is allowed per lite up to 6 square feet; no more than 2 total defects are allowed per lites 6 to 35 square feet; no more than 3 total defects are allowed per lite over 35 square feet. These standards do not apply to hand-made products. Variations in texture, thickness, color, as well as the presence of visible scuffs, scratches, and random small and large (“ox eye”) bubbles are typical in mouth-blown glass and are not considered defects, but rather desirable “perfectly imperfect” characteristics that attest to its authentic hand-made nature.

For more information, please see Bendheim’s ASTM Glass Standards For A&D Professionals, Contractors, and Clients.