This document defines glass surface quality on optical components per MIL-O-13830.
SCRATCH: Any marking or tearing of the glass surface.
SLEEK SCRATCH: A hairline scratch.
CRUSH or RUB SCRATCH: A surface scratch or a series of small scratches.
DIG: A small rough spot on the glass surface similar to pits in appearance. A bubble is considered a dig.
Surface quality is to be specified by a number such as 60/40. The first digits relate to the maximum width allowance of a scratch as measured in microns. The next digits indicate to maximum diameter allowance for a dig in hundredths of a millimeter. Thus, as can be seen from the table below, a surface quality callout of 60/40 would permit a scratch width of .0024 inches and a dig diameter of .0158 inches. The size of a defect is to be measured through the use of an optical comparator.
or Bubble Diameter
|Dig or Bubble