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.
White Comets On Prints. May be caused by the calcium dust from the lump of preservative in the tube; also from lime that may fall from the ceiling while cutting the paper, trimming the prints or loading the printing frame, and from negatives that have been improperly washed after fixing; or, by particles of undissolved developing crystals. If a plate is not properly fixed or washed it frequently happens that hypo will form in small crystals on the surface of the negative. Sometimes these crystals will not show for months after the negative is made. Negatives should always be examined and dusted with a soft camel's-hair brush before being printed from.
Wavy Markings. These will occur in prints if the developer is both weak and cold, or does not cover the print thoroughly during development. Always keep the print under the solution or spray the developer over the print with the hand.
Spots Different Sizes And Shapes. This is usually due to particles of dust or dirt in the developer. Never allow the developer to stand in your developing tray or open dish for any length of time, as dust will collect on the surface and cause not only white spots, but also black spots on the prints. It should always be returned to the bottle at once after developing. You should also stir the developer after developing a print.
Overcoming Dampness In Negatives And Backing Pads.
On damp days re-dry negatives by holding over a gentle heat, also dry the backing pads and be careful not to expose paper too long to the moist conditions of atmosphere before placing in the printing frame. In damp weather prints should be developed immediately after printing.
Black Comets And Brownish-Black Stains. These are generally caused by mercury and are usually produced when printing from negatives that have been intensified. Great care should be taken that intensified negatives are thoroughly washed before setting up to dry. Keep the mercury solution away from platinum paper. Mercury spots have a brown color; iron spots have a black color.
Note. A large majority of failures are due to carelessness in the manipulation and a general lack of cleanliness in every department. With clean rooms, tables, trays, and, above all, clean hands, one will experience little trouble in handling platinum paper. Black paper should be kept separate from sepia paper. It is always advisable when printing with both black and sepia paper to print black paper first, because if you print your sepia first there are liable to be particles of mercury on the negative that come from the sepia paper. It is also advisable, in case you print sepia paper from a negative before you print black, after you are through printing to wipe the negative with a piece of cotton; especially so if the negative has been varnished, as particles of dust stick to varnish more than to film.