There should be at least three acid baths, consisting of one part muriatic acid to sixty parts of water and the acid should be chemically pure. The print is placed face downwards in the first bath for five minutes, then removed to the second, where it should remain for ten minutes and then to the third, where it should remain for fifteen. Fresh acid baths should be prepared for each batch of prints and the old baths thrown away. The prints should now be washed in three changes of water, turning them carefully, so as not to rub their faces and to neutralize the effect of the acid a few grains of sal soda should be placed in the second washing water. One-half hour is sufficient time for washing and the prints can be blotted off and placed away to dry, or they can be mounted while still damp. The Bradley paper requires but one acid bath, in which it should be left for ten minutes.

The Willis & Clements paper is made in three grades, known as A A, or "thin smooth;" B B, or "heavy smooth" and C C, or "heavy rough." It is also made to produce black or sepia tones. In working the sepia paper the same general directions are to be observed as for black but the sepia paper is more sensitive to light, the temperature of the solution increased to 1500 to 1600 F. and sepia tablets are added to the developing solution, The Bradley paper is made in two grades, known as J, or smooth surface, and B, or heavy, slightly rough.