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TM 9-254
9-8.
Decoating Optical Components.
WARNING
o Sulfuric and boric acids are highly corrosive and react quickly on the skin and clothes. Repair
persons should wear rubber gloves, rubber aprons, and goggles. A safety shower or other
means should be provided for quick washing in case of an accident.
o The decoating process should be carried out under a ventilated hood, which will draw off any
corrosive vapors.
a.
Procedures for Decoating.
(1)
Mix a solution of 5 grams boric acid crystals in 150 cubic centimeters of concentrated sulfuric acid.
(2)
Place lens elements in a pyrex baking dish lined with a fiberglass cloth.
(3)
Insure that the acid solution and the lens elements are both at room temperature. Carefully pour a
sufficient amount of the acid solution into the pyrex dish to completely cover the lens elements.
(4)
Place a glass thermometer in the acid solution to monitor the temperature. Position the dish on a hot
plate, under a ventilation hood, and heat to a temperature between 230 and 250 degrees Fahrenheit.
(5)
After approximately 30 minutes, turn the hot plate off and allow the acid solution and lenses to cool.
(6)
When the acid solution has cooled to room temperature, use a battery acid syringe to transfer the acid
from the dish into a suitable storage container. This acid solution can be reused until it becomes too
weak to remove the coating from the elements.
(7)
Remove the lenses individually from the pyrex dish, wash them in luke-warm water, and dry with
cheesecloth.
(8)
After drying the lens elements, they should be checked for defects. Should any defect be found the lens
element should be marked with a wax pencil and sent to be reground or repolished.
9-9.
Coating Optical Components.
a.
Reasons for Coating. The principle reason for coating optical components of fire control instruments is to
increase light transmission, resulting in better visibility of the target. The coating will also reduce haze and ghost images
caused by internal reflection in the instrument.
9-25
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