To Find The Cause Of Pinholes. Pour one ounce of the bath into a glass graduate, and add, slowly, a drachm at a time of pure water to the solution. If, on adding one or two drachms of water, the solution turns milky, the holes are caused by an excess of iodide, which at once remove by pouring your entire bath into an equal quantity of pure water, allowing the iodide to settle to the bottom, and filter, and either boil down the bath to forty grains per ounce or add new silver. If, on the contrary, you can add from one to four ounces of water, and the solution does not turn milky, the pinholes are caused by a lack of behave handsomely and satisfactorily. Knowing these conditions, then, obey them, and your results will be what you desire. If they are not, there is a cause, and the sooner you think it out, look it up, and eradicate it, the sooner you will be happy.
As the remedies in all of the above instances are very obvious, I will only give the treatment for removing them from an old weak bath. Say your bath is a twenty-ounce one, pour it into twenty ounces of ice-water; a canary - colored, cloudy precipitate will be the result. Allow it to settle, then Alter the solution clear. You may now either add to it two ounces of nitrate of silver, or boil it down to twenty ounces of solution, when it is again as good as new. The above treatment will restore a badly-working bath almost without fail. If it does not, waste no time, but make it into a printing-bath by neutralizing the acid in it with ammonia; the iodide remaining in it may or may not be removed, as it does not seem to affect the tone of the prints. - C. A. Zimmerman.
My process consists in adding five drops of chemically - pure hydrochloric acid to every hundred ounces of the bath, and stirring it thoroughly for some time, then filtering it. By this means the excess of iodide of silver will combine with the chloride of silver, and, throwing it down, leave us a bath that will give clear negatives without any of the so-called pinholes. For every drop of hydrochloric acid added to the bath an equivalent amount of nitric acid is set free, probably rendering the bath too acid. In order to neutralize the a<i 1 and bring the bath to its original strength, the best way is to add carbonate of silver, which is taken up by the nitric acid, setting carbonic acid free, and forming again nitrate of silver. In order to prepare the carbonate of silver in a simple way, add a solution of chemically-pure carbonate of soda to a solution of nitrate of silver so long as a precipitate is formed, which is to be thoroughly washed and dried at common temperature. I use the carbanate of soda in preference to the carbonate of potassa on account of its being more easily obtained in a pure state. - J. Traill Taylor.
When my bath becomes charged with alcohol and ether, but works well otherwise, I pour it into a bottle containing one - third its bulk of water; filter, neutralize with liquid ammonia, and pour into an evaporating-dish, and boil down to its original strength. Filter, and add nitric acid sufficient, and it is ready for work again. But if the bath has become contaminated with organic matter, it will be best to boil it down and fuse it; then redissolve in purified water, acidify, and it generally works better than a new bath. Keep three or four baths on hand, and while you are working one have the others in the sun, after being first treated as above. - J. A.W. Pittman.
181. One of the great secrets in making nice, clean negatives, is to keep your chemicals at an even temperature both winter and summer; and in order to do so, make a wooden box, or, better still, have your tinner to make you one out of galvanized iron, large enough to hold your baths, having a V-shaped trough back of the baths for the receptacle of ice in summer, and made so as to lift out in order to empty the water in the morning, then replace should never be below 55° or 60°), and, also, by too thin or old and insensitive collodion.