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.
Loading The Plate-Holder. The wet plate, as its name implies, must be exposed while in its wet condition. After the plate has been in the silver bath a sufficient length of time, it is ready to be placed in the holder. Draw the plate from the bath slowly and carefully, slightly tilting it to one side, thus permitting the excess silver to drain back into the bath; then, catching the plate by two opposite corners, place it into the plate-holder in the usual way, when it is ready to be exposed.
Exposing The Plate. Having focused on the ground-glass the object which you wish to photograph, place the plate-holder in position, close the shutter and draw the slide. In order to test the rapidity of your bath, proceed in the following manner: Make a test by exposing two or three plates, ranging in time from ten to forty seconds. Keep a careful memorandum of each plate and exposure, and compare the results after developing. Remember that plates prepared with silver iodide may require twelve to twenty times the exposure of an ordinary dry plate, while those which have been prepared with bromo-iodide, or with collodion which is bromo-iodized, according to the formula described herein, will be much faster. One advantage of the wet plate, like the slow dry plate, is the great latitude of exposure allowable - you may over-expose considerably without any serious results.
Caution. For the benefit of those unaccustomed to handling wet plates, but familiar with the handling of dry plates, we would advise never allow your fingers or anything else to come in contact with the coated side of the plate. The film is extremely tender, and even a strong flow of water will often destroy it completely.
Developing The Plate. Into a graduate or large-mouthed bottle, pour sufficient developer to cover the entire plate - usually from three to five ounces being sufficient. Remove the plate from the holder and hold it by one corner with your left hand over the sink. With the developer in your right hand, flow the plate with a sweeping motion, spreading it over the entire plate in one operation. It is important that the entire plate be covered with one sweep. To do otherwise would give you streaks, and as the developing solution is inexpensive a liberal quantity should be employed. With a little practice you will be able to flow the plate successfully.
916. After the developer is flowed over the plate, slightly rock it backward and forward, thus keeping the developer in motion over the plate for twenty to thirty seconds. If the image flashes up quickly and is of an even gray color, you have over-exposed; but, on the contrary, if it builds up slowly or in black and white patches, you have under-exposed. This is, of course, supposing that all previous operations have been properly carried out. The appearance of the properly exposed plate is similar to an ordinary dry plate which has been bleached in mercury. When viewed by transmitted light it is of a brownish color, and of a creamy color when examined by reflected light. Examine the plate for density by holding it before the orange light, and unless you have carried the developing far enough the plate will not appear sufficiently dense. Rinse the plate under the tap of running water and again flow with developer. With a little experience you will soon be able to judge the proper density to which the plate should be carried in the developing.