After trying one of these remedies, if the bath refuses still to yield good results, more nitric acid should be added, until the solution will turn blue litmus paper slowly red.
I have never known a silver bath to fail to come to terms under this treatment. p31
The silver solution, when in constant use, rapidly deteriorates, and unless there is a very large quantity, it will soon become unfit for use, and however much or little there may be, it is only a question of time as to when it will cease to act satisfactorily.
This result is caused partly by the gradual contamination of the solution by the alcohol and ether washed from the collodionized plates that have been sensitized in it. When the bath is seriously affected in this manner, it is indicated by the difficulty experienced in getting the developer to flow evenly over the plate, and also by the strong alcoholic odor of the silver solution.
The necessity for a change of the bath may be delayed for a time by the addition of alcohol to the developer, which causes it to flow more evenly.
Another source of evil to the bath is the continual absorption from the surfaces of the plates immersed of minute portions of the salts with which the collodion is excited. After the silver solution has taken up all it can dissolve or assimilate, the surplus is held in suspension and is called free iodide, which deposits itself on the surfaces of the plates, and when in quantity causes the plate when taken from the bath to appear as if fine sand had been sprinkled over it. These small crystals prevent the action of the light on the parts they cover, and when the plate has been developed and fixed, every crystal has produced a small transparent spot or pinhole, as it is termed, and many a lovely negative has been ruined by pinholes.
This trouble may be cured by increasing the quantity of the solution and adding more silver nitrate, which, if in sufficient quantity, will dissolve the free p32 iodide. But if it may not be convenient to do this and no other solution is ready for use, then, after immersing your plate, tip the bath dish back so that the face of the plate may be inclined downwards, when the crystals will be deposited on the back of the plate and do no harm.
The silver bath is also contaminated with organic matter, taken up from the edges and backs of the many plates used, of which some portion of the albumen is likely to be exposed to the action of the solution, and also from dust, etc., falling into the bath dish, which will be taken up and held in solution by the acid in the bath, but when the acid can hold no more in solution, its presence will be indicated by a greyish white vail forming on the surface of the plate when developed; this is called fog, and may only partially obscure the image, or it may completely veil it.
The fogging of the plates in this manner may be prevented for a time by adding more nitric acid to the bath, which will dissolve the organic matter and prevent its deposition on the plate.
When the silver bath has, from long or much use, become seriously affected by any of these evils, it should be set aside and a fresh bath put in use, until an opportunity offers to thoroughly cleanse and renew the old solution, which can be done by one series of manipulations, as thus: