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.
Persulphate Of Ammonia Not Reducing. If the persulphate of ammonia bath is prepared properly, and is of good quality, it reduces. If it acts slowly strengthen by adding more persulphate. (See paragraph 277, Pari I.)
Persulphate Of Ammonia Bath Reducing Too Quickly. If the persulphate of ammonia reducer acts too quickly, it is because the solution is too strong. (See paragraph 275, Part I, Negative Reducing.) Always make up the bath just before you are going to use it.
Parts Of The Negatives Reduced With Persulphate Stained. If parts of the negatives which have been reduced are stained, place the plates in the clearing bath composed of alum and sulphuric acid. Previous to this, however, the plates should have gone through the sulphite checking bath. Be sure that the negatives are properly fixed and washed, and there will be no stain after reducing.
Plates Very Glossy After Reducing. All plates will appear rather glossy after reducing, and are, therefore, harder to retouch and etch. The cause of this glossy appearance is that the reducing solution acts on the top of the film, and actually cuts away a portion of this film. At the same time it acts as an astringent, and draws the little globules of gelatine together, thus causing the hard, shiny surface. This can be overcome to a certain extent by soaking the plate for a few minutes in a carbonate of soda bath, about sixty hydrometer test. This will open the pores, and there will be very little gloss.
Confining Solution To Only The Parts To Be Reduced. To avoid reducing other parts than those you desire reduced, mop the surplus water from the parts to be reduced. The solution will then attack the film quickly. Work carefully, applying only a little reducer, allowing it to remain on the parts to be reduced for only an instant at a time. Rinse after each application, and do not use too strong a solution. It is necessary that you act quickly. You must think and act at the same time. Practice, and practice only, will enable you to overcome this difficulty.