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Dear Martin and Andrew, The standard layout for developing (processing) print paper is:
Developer (always an alkaline solution)
Acid Stop Bath (dilute vinegar solution (acetic acid)).
Acid Fixer tray
Wash tray You can skip the stop bath however, its purpose is to stop development dead in its tracks and it protect the fix bath (extents its life) from the harmful neutralizing effects of the alkaline developer. The developer is a reducing solution. It reduces (splits apart) exposed silver salts into their two component parts, silver and a halogen. The silver remains on the paper to form the image, the halogen goes into solution. This action dilutes the developer. The reducing agent has an affinity for oxygen. Spent reducing agents oxidize and become staining agents. The developer contains preservatives to retard aerial oxidation and to neutralize the staining agents. As the print is moved to the next solution, some spent developer is carried with the paper. Some carryover remains in the stop bath but some continue on to the fixer. The fixer (hypo) contains a sulfur compound. Sulfur attacks silver over time, and causes it to tarnish and turn brown. A used fixer contains developer carryover with its staining agents. The fixer is a solvent for undeveloped silver salts. When the print paper emerges from a good fixing bath, the paper contains residue fixer. If not completely washed off the staining agents in the spent fixer will stain the paper yellow. It is necessary to wash the paper (film too) in running water to remove all traces of the fixer. Otherwise, yellow staining will result. Modern papers are over coated with a resin (actually now a poly-plastic and not a resin). This overcoat waterproofs the paper. Since paper is made from wood pulp it has a cell structure that absorbs fluids like a sponge. Without the over coat the wash time will be 1 hour for thick papers and ½ hour for thin. Washing time can be reduced to minutes with a suitable pre-wash bath in hypo clearing agent (a salt like solution that neutralizes spent fixer). The overcoat always violated at the edges when the paper is cut to size. This happens during packaging so you can’t do a thing to mitigate this. Spent solutions will be absorbed into the paper from the cut edges. Only copious washing after the fix or use of a suitable hypo clearing agent will prevent yellow edge stain. Sorry, paper making and chemical processing remains both an art and a science. Rub-a-dub your prints in a tub. Alan Marcus
ammarcus@earthlink.net
September 21, 2006
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