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.
Strength Of Solution To Use. The reducing solution must be used diluted, because the action of the solution begins on the surface of the film, and works its way through, and, if too strong, in all probability would dissolve away some of the shadow details before accomplishing the required reduction in the denser parts of the negative. Too strong a solution will also work too rapidly for even reducing, and one is almost sure to produce blotches and spots, instead of gradually blended results. Great care must be exercised lest you touch other parts of the negative, which do not require reducing. A good plan is to pour into a saucer a small quantity of the reducing solution, made according to instructions (see paragraph 265, Part I), diluting the solution by adding an equal amount of water. Dip the brush into this solution, and squeeze out the overflow of the brush on the edge of the saucer so that there will be but a trifle remaining on the tip of the brush.
Applying The Reducer With The Brush. Hold the plate to the light so that you can see through it. If possible, have the light lower than the plate so that you can hold the plate almost flat when applying the solution. Before applying the solution, however, mop the surplus water from the surface of the plate with a tuft of cotton, or with the ball of the hand. This will prevent the solution from spreading. When applying the reducer do not allow it to touch any other portion except the parts to be reduced, and allow the solution to remain on the plate only a few moments at a time. After each application rinse off with water, thereby avoiding the spread of the reducing solution, and the danger of reducing too fast. Examine the plates carefully after each application. After you have applied the weak diluted solution a number of times, and have not obtained the desired result, apply a stronger one, working very carefully. It is safer to work slowly, as your results in the end will be much better, and there will be less danger of reducing parts that should not have been reduced.
Use Running Water To Check Reduction. Always have running water from the faucet flow over the plate as soon as the reduction is carried far enough. This necessarily requires very quick action on the part of the operator, or the solution will be left a second too long, and the reduction carried too far.
Avoid Granular Surface By Returning The Plate To The Hypo Bath. After the parts are reduced to your satisfaction, rinse the plate for a moment under the faucet, and then replace in the hypo bath for ten minutes. This will insure a good color to the plate, and will produce a smooth surface instead of a granular effect, which would be the result if the plate were not returned to the hypo bath after the red prussiate had been applied.
299, Applying the Reducer with the Finger, or Tuft of Cotton. - Another very good plan, especially where you are reducing white drapery, is to apply the solution with the finger, dipping it in the solution and rubbing the parts to be reduced. Here again it is necessary to guard against rubbing these portions too hard. You should have running water during the process, so that you can quickly place the plate under the faucet after each application. For very delicate work, however, we advise using a No. 2 camel's hair brush; for heavier work you can apply the solution with the fingers, or tuft of cotton. In this way you can reduce strong highlights on the face, hair and drapery, but you must be exceptionally careful when applying the solution to the face that you do not overdo the work. When using the finger rub lightly or heavily, as may be required, but always bear in mind that it will not do to rub too hard. The sense of the touch will aid you in judging the amount of the reducing you are doing, as the film not only becomes thinner to look through, but really reduces in thickness. The sense of touch serves as a very good guide to prevent you from overdoing the reduction, or injuring the film by hard rubbing.
300. There are times when one would like to blend the drapery from the strongest highlights to total black shadows. This can be accomplished very nicely by applying the solution very lightly to the strongest lights, and gradually heavier to the parts requiring more reduction. A tuft of cotton is best for this work, as the reducer must be spread more broadly. While the majority of the reduction is in the lower portion of the plate one must occasionally swab, very lightly, the upper portions, rubbing heavier as you approach the lower parts, so as to gradually blend them. This blending will require considerable practice to do the work nicely, but when one gets the knack of doing it any desired result can be obtained. If the parts you wish to reduce are very strong, and the reducer does not take hold properly, use a double strength solution. When using the double strength solution hold the plate perpendicular, and apply to the lower parts, first blending upward. The reducer will then run over the parts to be reduced the most, and by constantly swabbing with the cotton, streaks will be avoided.