The Silver is very important that the silver bath should be made from the purest materials. The water especially should be carefully filtered and purified. The most efficient method of accomplishing this is to take distilled water, or transparent ice melted; add to it a few crystals of nitrate of silver, put into a bottle of white glass and set in the sun. In a few days it will darken corresponding to the amount of organic matter contained in it, which will be precipitated and can be filtered out. Make up a sufficient quantity to fill the bath holder of the size determined upon. This may be a flat dish—which will call for a less quantity of silver, but not on that account more economical—or a regular glass holder with box and cover, which is greatly to be preferred, being much more easily managed in respect of the plate, but also for keeping the bath in better condition (see Fig. 363). A size II x 13 will be found a serviceable and convenient size to work with. This will require ioo ounces, which should be of the strength of 4o grains to the ounce, tested by an argentometer (Fig. 364). Put this quantity into a large bottle of white glass, add to it a few drops of concentrated anmmonia, to neutralize, until it just turns red litmus paper blue, and set it in the sun for several days to clear. Any organic matter contained in it will be precipitated, or adhere to the sides of the bottle, which must be thoroughly filtered and cleaned out. Filter again and again until assured of being thor oughly pure, by its remaining clear. When ready for use, put into the bath holder, add a few grains of iodide of potassium-5 grains will be sufficient—and of nitric acid. C. P., a few drops at a time, until it turns blue litmus paper a decided red, when it will be ready for use. In place of adding 6 grains of iodide of potassium, a collodionized plate may be placed in the bath and allowed to remain over night, when sufficient of the iodide will have been communicated to it from the collodion.
The Care of the care of the bath is a matter of much importance, as it is liable at times to go out of order for causes not easily discoverable, there being many that affect it, which may set their evil influences into operation suddenly; hut the chief source is from organic matter introduced through the medium of the collodion and the glass plate, and should be care fully guarded against. In time it will have become so surcharged with alcohol and iodine from this source as to require doctoring, which condition may be known by the developer flowing over the plate as if meeting with a greasy resistence, and later by minute pin-holes like star dust being observable in the negative. The first of these may be corrected for a time by the addition of a little alcohol to the developer; but be assured that the other is not far away, and then it will be need ful that drastic measures must be adopted. To this end take a quantity of pure distilled water, or melted ice purified, equal to the bulk of the bath; pour the bath into it, filter out the iodides and simmer down by gently boiling in a granite or porcelain dish (Fig. 365.) until it is reduced to considerably less than the
original bulk. This operation will have evaporated out the alcohol. Let it now be brought to the strength of 4o grains to the ounce, by the addition of pure water, neutralized by the addition of a few drops of concentrated ammonia, and set in the sun, where the organic matter will be precipitated, and may be filtered out. A longer sunning and filtering will further improve it, and after assurance by its remaining clear, it may be acidified as at first, and again put to work.
Because of the liability of the bath to go out of order, it is well to have one or two distinct baths under process of sunning and purifying, besides the one in use, and so save disappointment at inopportune times Before beginning the work of the day the bath should be skimmed over with a piece of clean blotting paper.
The Dark-Room.—The dark-room should be arranged with everything so conveniently placed as to be readily found in the dim light necessary. This need not be so very dim, however, as to become a source of confusion, the wet-plate not being nearly so sensitive as the gelatine dry-plate of the photo grapher ; but the light must be made non-actinic in character, by being strained through a colored medium, either of glass, cloth or paper, that it may not affect the sensitized plate while it is being taken out of the bath and placed in the camera-holder.
If the light is taken from an outside window, it may be partly blocked out, while a portion may be covered with orange colored cloth or paper. A clearer light will be obtained in which to observe the action of the developer, by placing a pane of ruby-colored glass into a section of the sash. If dependent on gas or artificial light it should be enclosed in a lantern or other enclosure, and protected by ruby or orange-colored glass. The incandescent electric light is very convenient when it can be readily obtained. The sink and water-tap should be so placed with relation to the light as to be readily accessible at the moment development is seen to have reached the desired amount of detail.
Sensitizing the Hate.—The bath having been prepared and in working order, the next operation is to make sensitive to light the glass plate. This having been flowed with the collo dion as described is laid on the dipper, and a steady, unhesitating motion, lowered into the bath, stirring it a few times, but not raising it so high as that any part of it will be out of the solution. This may be done with the full light up in the dark-room ; but in placing the plate into the bath let it be shaded by the person or otherwise, until the cover is placed over it, otherwise "fog " may be the result. It should be allowed to remain in the bath until sufficiently sensitized, for which five minutes is about right, though with a bath that has been some time in use a few minutes more will do no harm.