The glass industry standard is set by the ASTM (American Society of Testing & Materials). ASTM glass standards cover a wide variety of glass issues such as visible glass defects. Anyone can find imperfections in the glass if they look close enough and hard enough. Glass is meant to be looked through, not at. Glass is not perfect.
ASTM Visual Inspection Criteria:
- 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.
- Glass shall be inspected in the border area in transmission and reflection at a distance of 10 ft from the observer.
- The glass must be inspected using a viewing angle of 90 degrees from the glass with a suitable background light (daylight without direct sunlight or a range of 500 – 1000-foot lamberts.)
- Inspection should not exceed viewing of more than 5 seconds for lites up to 6 square feet, 10 seconds for lites up to 35 square feet, and 20 seconds for lites larger than 35 square feet, either in transmission or reflection.