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104 Transactions of S.M.P.E., March 1926
the slats, so that the developer is renewed most rapidly at these points, resulting in an increased rate of development.
Curved markings, as shown clearly in Fig. 5, are also produced as a result of curling of the film between the bars, which causes the developer to flow more or less in specific channels.
Reel bar marks may be minimized by using a reel with as many slats as possible so that the cross section approximates to a circle, by avoiding rapid rotation of the reel, and by reversing the direction of rotation of the reel at intervals.
Airhell Markings
When a strip of motion picture film is immersed in a developer or other solution, there is always a tendency for more or less air to be carried along with the film under the solution, where it immediately tends to assume a spherical shape resulting in a so-called airbell, see
Fig, 5. Bar Markings Produced when Developing Film on a Reel
Fig. 6. The bubble of air usually clings to the film throughout the course of development unless for some reason it is dislodged, and it prevents access of the developer so that on subsequent fixation a clear spot or airbell marking remains. Sometimes the airbell persists throughout fixation or is formed again on immersion of the film in the fixing bath, so that after washing a spot of unfixed-out emulsion remains.
Clear airbell markings produced on negative film appear as dark spots on the positive, and in view of the present practice of developing negative film on racks and positive film on processing machines, which do not have so great a tendency to give airbells, most airbell markings seen on the screen at the present time are dark spots caused by airbells on the negative.