Contact us

Scratch / Dig Specifications

Purpose:

This document defines glass surface quality on optical components per MIL-O-13830.

Definitions:

  • 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.

Procedure:

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.

Scratch or Dig Number Maximum Scratch Width Maximum Dig or Bubble Diametre Dig or Bubble Separation Distance
mm   Inch
mm   Inch
mm   Inch
120
0.12   0.0047
1.20   0.0473
20   0.787
80
0.08   0.0031
0.80   0.0315
20   0.787
60
0.06   0.0024
0.60   0.0236
20   0.787
50
0.05   0.0020
0.50   0.0196
20   0.787
40
0.04   0.0016
0.40   0.0158
20   0.787
30
0.03   0.0012
0.30   0.0118
20   0.787
20
0.02   0.0008
0.20   0.0079
20   0.787
10
0.010  0.0004
0.10   0.0039
1   0.040
05
0.005  0.0002
0.05   0.0020
1   0.040
03
0.0030.00012
0.03  0.0012
1   0.040
Scratch or Dig
Number		 Maximum Scratch
Width		 Maximum Dig or Bubble
Diametre		 Dig or Bubble Separation
Distance
mm        Inch
mm        Inch
mm        Inch
  120
0.12      0.0047
1.20      0.0473
20      0.787
  80
0.08     0.0031
0.80     0.0315
20     0.787
  60
0.06     0.0024
0.60     0.0236
20     0.787
  50
0.05     0.0020
0.50     0.0196
20     0.787
  40
0.04     0.0016
0.40     0.0158
20     0.787
  30
0.03     0.0012
0.30     0.0118
20     0.787
  20
0.02     0.0008
0.20     0.0079
20     0.787
  15
0.015     0.0006
0.15     0.0059
20     0.787
  10
0.010     0.0004
0.10     0.0039
1     0.040
  05
0.005     0.0002
0.05     0.0020
1     0.040
  03
0.003     0.00012
0.03     0.0012
1     0.040
Scratch or Dig Number Maximum Scratch Width Maximum Dig or Bubble Diametre Dig or Bubble Seperation Distance
mm                      Inch
mm                      Inch
mm                      Inch
      120
0.12                    0.0047
1.20                    0.0473
 20                    0.787
      80
0.08                    0.0031
0.80                   0.0315
20                   0.787
      60
0.06                   0.0024
0.60                   0.0236
20                  0.787
      50
0.05                  0.0020
0.50                  0.0196
20                  0.787
      40
0.04                  0.0016
0.40                  0.0158
20                  0.787
      30
0.03                  0.0012
0.30                  0.0118
20                  0.787
      20
0.02                  0.0008
0.20                  0.0079
20                  0.787
      15
0.015                  0.0006
0.15                  0.0059
20                  0.787
      10
0.010                  0.0004
0.10                  0.0039
1                  0.040
      05
0.005                  0.0002
0.05                  0.0020
1                  0.040
      03
0.003                  0.00012
0.03                  0.0012
1                  0.040