This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Double And Blurred Images. Double and blurred images will occur, when making time exposures, if the object moves; or the camera itself may have been moved or shaken during the exposure. For all time exposures the instrument must remain perfectly rigid (unmoved) during the exposure. It is very essential to have a tripod, although for interior work it is feasible to set the camera on a small table or stand and secure satisfactory results, but the tripod is more convenient.
Streaks And Light Spots Caused During Development. Difficulties will occur when the film has not been properly - i. e. completely - immersed in the developer at the very start. Soak the film, for half a minute or so, in clear water, before placing it in the developer, thus softening the emulsion to a certain extent and wetting its surface so that the developer may immediately begin its action on all portions at identically the same time. Place the film in the developer with the emulsion (dull) side down and keep it moving in the developer.
White Spots On Film After Fixing. This would indicate that the film was not entirely immersed in the hypo, or that parts of the film had become stuck together, thus preventing these white portions from becoming fixed. Always handle and separate the film a few times during fixing.
Pencil Lines On Film. These are caused in two distinctly different ways: First, if there is any dust in the camera or if the rollers over which the film runs are not absolutely smooth, the film will be scratched or the dust in the camera, collecting on these rollers, will cause black scratches and streaks longitudinally across the developed film. Second, should you draw the film with the emulsion side down through the developer, so that the film strikes the bottom of the tray, it is likely to be scratched. Abrasion marks will immediately appear, which reproduce in the finished print as white lines.
236. Since there is no way of remedying these lines and streaks upon the film, exercise the greatest of care, when developing the film, not to allow its surface to come in contact with anything excepting the solution. In fact, this caution must be observed during every stage of the handling of the film, from the removal from the camera to the placing in the printing frame. Do not allow your fingers to come in contact with either side of the film, even when it is dry. When it is necessary to handle the film, take hold of the extreme edges only. All films on the market at the present time are non-curling, and during the process of manufacture, in order to make them non-curling, both sides of the celluloid support are coated with gelatin. The gelatin on the back of the film, however, is not sensitized, but is merely a coating to keep the film from curling.