Submitted by Al …
(Adapted from The Encyclopedia of Photography ©1963)
Air bells are tiny bubbles in developing solutions, which often cling tenaciously to the gelatin film or to paper emulsions and cause small circular or elliptical clear spots to occur. A spot having soft edges or one of low density indicates that the bubble grew smaller as development progressed or broke before development was completed.
These annoying defects can be avoided by breaking the bubbles as they gather on the film or paper surfaces. In light-tight tank development of film, air bells can be broken by agitation; turning the reel or raising or lowering it once or twice or, in some cases, turning the tank upside down several times during agitation. The method depends on the type of light-tight tank being used. When developing in an open tank, air bells can be broken by passing the fingers over the surface of the film when it is first covered by the developer; this also applies to paper development. If your equipment and procedures permit, the best way to eliminate air bells is to lift the film or developing reel completely out of the solution for a few moments at the beginning of development. It is easy to do this if you are developing paper. The pressure of the atmosphere and the running off of the developer will break the tiny bubbles.
Other ways of eliminating air bells consist of adding a small amount of wetting agent to the solution and, in some cases, soaking the film in water before development. The latter procedure is not recommended with modern films since it may cause a loss of sensitivity.
Comments