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.
Blisters. The printing frame has been placed too near the source of light. This would be indicated if the negative felt rather warm to the touch when taking the print out. In this event, the print should be allowed to cool off before developing. Prints may have been creased or broken while washing. Do not allow the water to run directly on the print from the tap. Too great a variation in temperature between the different solutions and the wash water may also be responsible for this trouble. It may also be due to an insufficient quantity of acid in the fixing bath. The fixing bath must be kept acid. It must be borne in mind that each print going from the developer into the fixing bath carries a certain amount of the alkali contained in the developer, which in time will neutralize the acid. Prints will sometimes blister when not allowed to remain in the fixing bath long enough to harden the film. The surface of the print when removed from this bath should not be slippery to the touch.
Impure Chemicals. It is easy to ascertain when the fixing bath is not in proper condition, by wetting the thumb and index finger in the fixing solution. If the two fingers do not slip easily when rubbed together, the fixing solution is right.
Discoloration Around Edge Of Prints. If the centre of the print is clear, it indicates that the paper has been kept in a place exposed to chemical emanations, such as ammonia vapors, illuminating gas, gas from a furnace or stove, or fumes from turpentine or sewer gas. The package of paper must be kept tightly closed when not in use.
Curling And Cracking Of The Surface. The paper has become too dry. It should not be kept in a hot, dry place. The trouble may be overcome by soaking the prints for a few minutes in a bath consisting of one ounce of glycerine and twelve ounces of water. Then dry the prints without washing them again.
Round White Spots. Some opaque substance between the paper and the negative when printing; air bubbles remaining on the surface of the paper while in the developing solution - the bubbles should have been removed with the finger during development. White deposit all over the surface of the prints is caused by milky hypo bath - if washed thoroughly, it can be removed.
Black Surface Marks Or Scratches. This occurs principally with glossy paper, and is the result of pressure or friction before development. These marks can be removed from the dry print by rubbing with a tuft of cotton dipped in wood alcohol. This trouble may be made absolutely impossible by using Cyko Liquid Developer (Non-Abrasion).
Canary Yellow Color Produced When Cyko Liquid Non-Abrasion Developer Has Been Used. A sign that the print has not been fixed sufficiently. The canary color should disappear entirely when properly fixed in a correctly prepared acid hypo bath.
Freaks. Picture develops irregularly, and appears to be covered with greasy streaks and finger marks, giving the impression that they are spots on the paper which have never been coated. It is annoying to the photographer, because he feels sure that the fault is in the paper, which is not so. These freaks occur most frequently in warm weather when the humidity is great, and are due to the fact that the paper absorbs moisture unevenly, and becomes repellant in certain spots to the action of an incorrect developer.