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.
Exposing. Place your plate-holder in position at the back of the camera, being careful, however, that it is not unnecessarily jarred. Close the shutter and carefully draw the slide, in order to avoid dust. (For exposure, see Paragraph 913, Wet Plate Process.) After the exposure has been made, return the slide to the plate-holder in the same manner as you removed it. The length of exposure is governed by the speed of your collodion, strength of light and rapidity of lens used. Usually, from five to ten seconds will be necessary.
Developing. After making the exposure return to your dark-room and proceed to develop the plate. Developing "must be done at once, as the plate must be exposed and developed while it is wet. Close your dark-room door and hold the plate with the glass backing over the sink. The glass backing will hold the tin plate from buckling during development, and the latter is, therefore, much easier handled. Grasp it firmly at the left-hand corner with the thumb and first two fingers of your left hand. Pour the developing solution over the entire plate with a single sweep and gently rock the plate so as to keep the developer flowing to and fro and over the entire surface. This requires a little practice. Never pour on with a splash.
1022. In the sink underneath the plate you should have a bottle with a funnel. In this funnel place a little absorbent cotton. When the developer flows off the plate, it will flow into the funnel. The cotton will filter it and this developer may then be used when developing overexposures. You should strive to produce as near the correct exposure as possible. This you can only learn by experience and carefully watching your experiments. The exposure cannot be corrected by development, as is the case when developing dry plates. Should you know in advance that the plate is over-exposed, then by applying the once-used developer you will materially improve the results.
Development Of Ferrotype Plate. The image will begin to appear almost immediately upon flowing the developer on the plate. When the shadows appear quite clear the plate is fully developed and should be immediately rinsed with water. If the development is stopped too soon the picture will appear too black; if it is allowed to develop too long, the image will appear weak, flat and foggy. When rinsing, do not allow the water to run too strongly on the plate, as it is apt to damage the film. If the ferrotype has been over-developed and, therefore, appears weak and flat, you can improve it by adding a drop or two of iodine to the fixing bath. In order that your entire fixing bath does not become charged with iodine, pour a little of the regular fixing bath into the tumbler or graduate and add the iodine to this. Pour a sufficient quantity of this fixing bath over the ferrotype plate, in exactly the same manner as you did the developer, draining the surplus solution back into the tumbler to save for future use. With the image on the plate brought to its proper stage, rinse under the tap and place into the regular fixing bath.