Hi-Efficiency Coating No. 401
Specification No. 2016

Spectrophotometric curve shown in the visible region is measured at normal incidence.

*When the coated element is used at angles other than normal, curve peaks will shift toward shorter wave lengths (down scale). This variation is dependent on degree of angularity from normal incidence.

Scope
This specification applies to the above coating when it is applied to glass with an index of refraction of 1.523.

Materials and Workmanship

1. 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.
2. The coating shall have negligible absorption of visible light.

Reflection
The coated element shall reflect from the front surface 37 plus or minus *5% of the total incident light in the visible region as defined by a Viscor filter, when using an incandescent tungsten filament lamp light source.

Transmission
The coated element shall transmit 63 plus or minus *5% of the total incident light of above type in the visible region defined by the Viscor filter.

Adherence
No visible part of the 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.

Hardness
No evidence of film removal or film abrasion shall be visible to the eye when any one or all of the following test are applied:

1. 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. The temperature shall not exceed 80° F.
2. 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.
3. 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.

Durability
No evidence of film removal of film abrasion shall result from one or both of the following tests:

1. The coated element shall be placed in a thermostatically controlled cabinet with a salt atmosphere at a temperature of 95° F. plus or minus 4° 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.
2. 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 120° F. plus or minus 4° F. for a continuous period of 24 hours.

Water Resistance
No evidence of film deterioration visible to the eye shall result from the following test:

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.

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 500° F.

* This production tolerance can be reduced for special applications where closer tolerances are required.