Submitted by Al …
(Adapted from The Encyclopedia of Photography ©1963)
To prevent undue reflection of light inside of cameras, enlargers, and other photographic instruments— where absolute darkness is essential—many surfaces are treated by the manufacturer with what is known as blacking. This blacking will be found on the inside surfaces of most cameras, even on the moving parts. Lens mounts, film slides, and bellows must all be blackened to reduce the danger of flare from reflected light. When buying used equipment, special care must be taken to examine the quality, permanency, and extent of blackening. A lens barrel, for instance, must always be black inside. The same is true of other parts near the passage of light.
It is possible to apply blacking at home if necessary. If a homemade device such as a cardboard extension tube or wooden sensitized paper holder has been made, blacking should be applied. In all cases, be sure that the surfaces are clean before application. Rust, which is apt to appear in enlarger heads, or other areas where there has been excessive heat, should be especially guarded against.
There are many formulas and many methods for blacking. Aluminum and brass for instance, will not accept the same blacking solution, and they in turn, differ from the blacking necessary for leather or wood. In general, the idea is to have a permanent coating or a matte surface, meaning no reflections. Black paint is hard to use, as it often has a glossy sheen. Special matte black lacquers are made for this work. A good general blacking substance, according to Wall’s Dictionary of Photography, is a paste of lamp black and japanner’s gold size (various hard, durable, black varnishes, originally from Japan). For wood, a good black coating is ferrous sulfate, and once dry, followed by tannin solution.
Wall, in his Dictionary, also gives this procedure for blackening aluminum: clean the surface with emery or other fine abrasive, coat with olive oil, and heat over a spirit lamp until black. Another good all-around blacking is a mixture of vegetable black with turpentine.
The interior of lens mounts and shutters is always blackened to avoid scattered light from the marginal rays of light through the lens itself. Sometimes the beveled edges of internal glass elements are also blackened for the same reason. Looking into a lens, the photographer can sometimes see places where the blackening of the barrel or the lens edges has chipped away. He should not attempt to disassemble the lens to repair these spots. It is nearly impossible for the amateur to reassemble such a lens correctly and with the proper cleanliness. Where the inside of a lens barrel, of the edges of the elements need reblackening, the entire lens should be sent to the manufacturer or a reliable repairman to have this work done under the proper conditions and with the correct material.
Could you reassemble these lenses and ensure they work properly afterwards?
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