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.
Pin-Holes In Enlarged Negative, Which Are Hardly Visible In The Transparency. These pin-holes are caused by dust on the negative or transparency plate when making the transparency. When the enlarged negative is made these pin-holes are also enlarged, and will show very much exaggerated in the enlarged negative. Carefully dust the plates, negative, and printing-frame, also the inside of the camera, and this defect will be prevented.
Streaks And Marks On The Enlarged Negative. These are generally caused by dirt on the back or front of the negative or transparency. Be sure that both the front and back of the negative are perfectly clean.
Spots Transparent And Semi-Transparent That Are Not Caused By Dust. These are generally caused by particles of dirt in the developer, or air-bells gathering on the plate when first placed in the developer. A good plan is to keep a piece of absorbent cotton thoroughly saturated with developer in the developing tray, and to swab the entire surface of the plate with the absorbent cotton. This will remove all tiny air-bells and dirt.
Center Of Large Negative Seems To Have More Exposure Than The Edges. This is because the light is not evenly distributed on the ground-glass and negative, and will occur more often when using artificial light. To overcome this it will be necessary to place the light further away from the ground-glass.
Enlarged Negative Very Thin And Full Of Detail In The Shadows. This is a certain sign that the plate was over-exposed, that it was not treated according to exposure while developing, and was not developed far enough. It is always advisable to overdevelop an over-exposure, and then reduce, according to the instructions given in lesson on Reducing.
Transparency Very Thin, Shadows Filled With Detail. The remedy for the preceding difficulty also covers this one.
Enlarged Negative Very Grainy. If the ground-glass or tissue paper is too near the transparency you are enlarging, or the negative from which the enlarged transparency is being made, the grain of the ground-glass or texture of the paper will show in focusing, and this will, of course, show in the enlarged negative. Transparencies which are under-exposed and then forced in development will also have considerable more grain than when they are properly exposed, and this grain will show stronger in the enlarged negative; therefore, aim for correct exposure for your transparency.