- The coating process shall cause no injury to the glass surface which would cause rejection of the optical element under other applicable specification. Any optical element which has met the requirements of other applicable specifications prior to coating shall not be rejected after coating because of fine hair lines or other defects in such optical element which are made more visible by the coating.
- The coating shall have negligible absorption of visible light.
The coated element shall reflect from the front surface 32 plus or minus *3% of the total incident light in the visible region as defined by a Viscor filter, when using an incandescent tungsten filament lamp light source.
The coated element shall transmit 68 plus or minus *3% of the total incident light of above type in the visible region defined by the Viscor filter.
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.
- The coated optical element shall be carefully washed first in a solution consisting of one (1) ounce of sulphated alcohol, one (1) ounce 15 Baume normal amomonium hydroxide, and one (1) gallon water; then cleaned in acetone or grain alcohol and dried with lens tissue or soft cloth.
- A thick past of U.S.P. precipitated chalk and water shall be applied to the coating and allowed to dry, and then wiped off with a soft cloth.
- A pad of clean dry cheese cloth (previously laundered) 3/8 inch in diameter, 1/2 inch thick, bearing with a force of one pound on the coating shall be rubbed across the coated element in any direction 150 times.
Note: During the above tests, care should be exercised to prevent contaminating abrasives contacting the coated surface causing slight sleeks.
- The coated element shall be placed in a thermostatically controlled cabinet with a salt atmosphere at a temperature of 95Â° F. plus or minus 4Â° F for 48 hours. The salt atmosphere shall be obtained by allowing a stream of air bubble through a salt solution containing about 1 1/2 pounds of sodium chloride per cubic foot of water.
- The coated element shall be placed in a thermostatically controlled humidity cabinet with an atmosphere of at least 95% relative humidity and at a temperature of 120Â° F. plus or minus 4Â° F. for a continuous period of 24 hours.
A drop (0.05 milliliter) of distilled water shall be permitted to dry at room temperature on the coated surface and the coated surface shall then be cleaned with acetone or grain alcohol.
* This production tolerance can be reduced for special applications where closer tolerances are required.