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.
Black Spots. Black spots, when they show a star or comet-like effect on paper in the first wash waters, are caused by small particles of iron rust in the water, which may come from the inside of water pipes, and are often caused by a sudden jar to the pipes in some portion of the building, setting free small particles of iron rust on the inside of pipes, also from iron pumps or iron roofs.
299. A good filter can be made by taking two thicknesses of chamois, and tying them around the faucet. The chamois does not allow the least particle of dirt to filter through, and can be washed and changed each day.
300. Black spots showing the same comet-like effect are often caused by using metal cut-outs. Small particles of the metal are ground off and settle on the surface of the prints. When wet, this metal will reduce the silver in spots. Dust each print carefully after trimming, face and back, or, better still, trim prints after they are toned. Never use a steel or iron cut-out. Celluloid cut-outs are the best.
301. Black spots may be caused by using enameled trays that are worn down or chipped, exposing iron parts. Prints coming in contact with these parts often show black spots, or rust spots. This is also the case where printers employ home-made oilcloth lined trays, using iron tacks or nails to fasten the oilcloth around the edge of tray. These nails rust and hands coming in contact with the nails carry the rust to the wet prints, causing black spots. Copper tacks should be employed to fasten the oilcloth on the tray.
Yellow Whites. (a) Yellow whites may come from prints not being toned far enough in the gold bath, or from trying to wash prints in running water between gold and platinum baths; or between platinum bath and hypo. Running water will not do. Prints should be washed by hand and the water changed.
(b) Yellow whites are sometimes produced by gold bath being too alkaline.
(c) If prints turn yellow in first wash water it is usually due to a trace of hypo from the hands or trays.
(d) The use of an old platinum bath, over and over, will frequently cause yellow whites.
White Spots. White spots are caused by insufficient handling in hypo bath and not handling in the washing water after fixing; also by not drying fast enough. Sometimes they are caused by drying between cheap blotters and newspaper stock. Undissolved hypo in the fixing bath will also cause small white and yellow spots.
Yellow Spots. Trouble of this nature may come from a number of causes, such as: Using impure or old blotters; insufficient washing after hypo bath; using old paste for mounting prints; impurities in mounts; slow drying of prints; or cheap manila envelopes containing chlorine, or other chemicals, which the face of the print is allowed to come in contact with.
305. The principal cause of yellow spots which show on the mounted prints, after they have been stacked and put away, is moisture in the mount. This moisture drawing through the stacked prints causes the bleaching chemicals and coloring matter in the mount to act on the paper, bleaching, and causing stains, or spots. Much of this trouble can be avoided by running prints through a hot burnisher with cardboard over face of print. By doing this the mount is thoroughly heated and dried out, which will prevent the trouble in almost every case. Rubber bands will also cause yellow lines on face of prints.