Chrome Glass Coatings
Specification No. 1069

Scope:
This specification covers the application of chrome coating on glass substrates for use in chemical etching where a high degree of resolution is required.

Material:

1. Select quality – All glass substrates will receive special selection and handling to insure the highest quality surface finish.
   1. Thickness – To be specified by customer
   2. Flatness – To be specified by customer
   3. Ultraviolet transmitting – Greater than 80% between 380-415 mu.
2. Chromium Coating
   1. The chrome shall be applied to one surface of the glass substrate without injury or change in the physical characteristics of the glass.
   2. Adherence – No part of the chrome coating shall be removed by the standard cellulose tape test.
   3. Test: The tacky surface of cellulose tape shall be carefully placed against the coated surface. It shall then be quickly removed with a snap action which exerts the greatest possible stripping action on the coated surface.
   4. Hardness – The chrome coating is noted for its hardness and is comparable to the underlying glass surface for resistance to nonabrasive cleaner and soft clean cloth.
   5. Note: Unnecessary cleaning will increase the risk of contaminating abrasives contacting the coated surface causing sleeks and scratches.
   6. Density – The coating shall be applied to one side of the plate homogeneously over the surface with a density of 2.5 or greater.
   7. Temperature – The coating shall not be adversely affected or damaged by exposure to ambient temperature of 40° F. to 200° F.
3. Allowable defects – Must be specified by customer. A defect is defined as any open void or pinhole, which only transmits light through the otherwise opaque chrome film, causing defective reproduction during standard chemical etching techniques. The allowable defects are graded according to maximum size allowable and must be specified according to resolution desired.

Grade A – Individual pinholes shall not exceed .0001" in size and shall be limited to one (1) such void within each square inch of the critical area of the plate. Pinholes less than .00005" shall not be cause for rejection.

Grade B – Individual pinholes shall not exceed .001" in size and shall be limited to one (1) such void within each square inch of the critical area of the plate. Pinholes less than .0002" shall not be cause for rejection.

Grade C – Individual pinholes shall not exceed .005" in size and shall be limited to one (1) such void within each square inch of the critical area of the plate. Pinholes less than .001" shall not be cause for rejection.

Note: Inspection for the above shall be performed in an acceptable manner which can be referenced to a known standard of micro measuring techniques.

Transparent 30-30 Chromium Alloy Type
Specification No. 1064

Structure
The splitter plate type mirror shall consist of a hard abrasion resistant adherent chromium alloy film applied by Thermal Evaporation in high vacuum to the surface of glass and shall have the following characteristics.

Transmission
The mirror shall transmit not less than 27% nor more than 33% of total incident light in the visible region.

Reflection
The mirror shall reflect from the front surface of the mirror film not less than 27% nor more than 33% of the total incident light in the visible region.

Adherence
No visible part of the mirror coating shall be removed by the cellulose tape test described here:

Test: The tacky surface of cellulose tape shall be carefully placed in contact with a portion of the coated surface and firmly rubber against that surface. It shall then be quickly removed with a snap action that exerts the greatest possible stripping action on the mirror surface.

Corrosion Resistance
There shall be no noticeable deterioration of the mirror film or image clarity after being subjected to the salt spray test described here:

Test: The mirror shall be placed in a thermostatically controlled cabinet maintained at 95° F. and continuously sprayed for 1000 hours with a fine spray of salt solution, which is made by dissolving 20 parts of sodium chloride in 80 parts by weight of distilled water.

Effect of Temperature
The coating shall function satisfactorily and shall not be damaged by exposure to an ambient temperature of minus 60° F. and plus 400° F.

Abrasion Resistance
The chromium alloy film shall be substantially as resistant to abrasion as the underlying glass. The mirror should withstand cleaning with any non-abrasive liquid cleaner and soft cloths without scratching, rubbing off, or loss of reflectivity.