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.
Difference Between Fresh And Old Paper. The paper when you receive it, if fresh, is in an acid condition, caused by the chemicals used to preserve it. In time these chemicals evaporate and as the paper grows older the amount of acid remaining in it is reduced. Therefore, fresh paper containing more acid must be washed more thoroughly than if the paper was old. You must remove the acid and preserving chemicals from the paper before it will tone, as the gold toning bath is an alkaline solution and must be kept in this condition while toning all prints. If all these acid properties are not removed from the prints before entering this bath, the acid will change the bath from alkali to acid and the prints will not tone, but will bleach. Old or well-ripened paper, therefore, will give you less trouble than fresh paper. We therefore advise when purchasing fresh paper, that you place it in a dry place and allow it to ripen for say two weeks before using. As in very warm climates, or during extremely hot weather, the paper will ripen much more rapidly, one week's drying will be sufficient.
Effects Of Acid Water. Where water is used which tests acid, you will have sulphurization and faded prints, unless provision is made against it. Many failures can be accounted for by lack of judgment, or absence of knowledge as to what to do and when to do it. If you have carefully tested the water you are using and find it is all right, and if you have handled the paper in all its manipulations in accordance with the above instructions, the trouble is doubtless due to defective paper. In some localities photographers are troubled with faded and bleached prints, and upon investigation it has generally been found that the water used was slightly acid. To tone with such water will invariably give bleached prints unless properly treated.
238. We advise you always to test the water to be used before beginning to tone. Water that tests slightly alkaline, or water that will neither turn blue litmus paper red nor red blue in a few minutes - in other words, neutral water - is all right. Water that tests acid must be first neutralized before using. Be sure to remember that the preserving chemicals used in preparing paper are very acid. This acid must be eliminated, but it cannot be done with acid water, no matter how thoroughly you wash the prints. Neutralize all wash water previous to gold toning, by adding to the first wash water 1/2 ounce of saturated solution of ordinary sal soda, or sufficient to turn red litmus paper blue in one minute, and to each following change of water add a little less. The last water use without alkali, as the prints are well saturated with it and the last washing will eliminate the excess alkali from the prints and place them in a neutral condition.
239. Prints entering the gold bath in an alkaline or neutral state will tone freely and evenly. After toning in the gold bath they can be placed in plain water without neutralizing it. As the next bath (platinum) is an acid solution, the prints can be in an acid or neutral state, but they must never be alkali when entering the platinum bath. For this reason be sure to wash the prints carefully in several changes of plain water after gold toning, in order to remove the excess of alkali obtained in the gold bath. The prints are then ready for the platinum bath, which will work nicely after this operation. Tone prints deep in this bath and after toning place them in plain water. If the previous wash water has proven to be acid this must also be neutralized with sal soda, and tested with litmus paper. The water now being neutral (and not acid) will check the toning and will also prepare the prints to enter the hypo bath.
240. After all prints are toned prepare your hypo bath in the regular way, being absolutely positive that it is alkaline. It must never be acid. If it is, neutralize by the addition of a few drops of carbonate of soda. Then fix the prints as usual. After fixing you can wash your prints in ordinary water. Even if the water is acid at this stage, it will do no harm.
241. A few facts should always be remembered: First, all wash waters must be neutral. Water but slightly alkaline will do no harm. Second, prints must be in an alkaline, or at least a neutral condition when entering the gold bath. Third, they must be in a neutral and not an alkaline condition when entering platinum bath, which is an acid solution. Fourth, they must again be washed into a neutral state - slightly alkaline will do no harm - before entering hypo bath. The latter must be alkaline. The condition of water for final washings is of no particular consequence.