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.
Collodionizing The Plate. On the supposition that you have made all preparations and are ready to make your exposure, you may now proceed to coat or collodionize the plate. Take one of the ferrotype plates and place on the tips of the thumb and fingers of your left hand, sufficiently spreading the fingers to balance the plate. (See instruction, Wet Plate Process.) With your right hand take your collodion bottle and pour some of the collodion in the center of the plate (about half the size of the plate), then, very slowly and carefully, slightly tilt the plate in the direction of the upper right-hand corner. Just before the collodion reaches the edge, tilt so that it will run very gently and smoothly toward the upper left-hand corner, then down along the edge toward the lower left-hand corner, and then over to the lower right-hand corner. Pour the excess of collodion into another bottle and allow the plate to drain. Rock gently from edge to edge - not back to front. This will cause the collodion to set evenly and prevent streaks. Just as soon as the plate begins to give a dull surface, the film will have been properly set. Touch the bottom corner, and if no longer tacky or sticky it is ready for immersing in the silver bath. In cold weather collodion will set much slower than in hot weather. It usually requires but a few seconds for the collodion to set.
Sensitizing. The collodion on the ferrotype plate, having been properly set, is now ready for sensitizing. Place the plate on your dipper and slide it with a gentle, continuous motion down into the silver bath. If there is the slighest pause or hesitation it will cause a line across the plate. It is a good plan to raise and lower the plate a few times after it is immersed. If necessary, carefully wipe out your plate-holder while the plate is sensitizing. In fact, it is a good plan to do so often, as dust is sure to cause all kinds of trouble. The sensitizing of the plate should be done with the door of the dark-room closed, using only the regular dark-room light. You may use considerable of this dark-room light, but it must be yellow or orange. Where the glass bath is enclosed in a box and has a cover, the plate may be dipped into the bath with the dark-room door open, but the cover must be immediately replaced.
1019. After the plate has been in the bath for about a minute or two, raise it from the bath and examine it before the orange light to see that all greasiness has disappeared. In cold weather it will take twice as long to sensitize the plate as it will in warm weather. If you find the waves or oily marks have not disappeared, lower the plate again, but very gently. When the plate appears quite even, dip it a few more times, very slowly. When your plate is properly sensitized, lift it to the top of the bath dish and allow it to drain for a moment. Next, place your plate into the holder. Set it in very gently, and place back of it a piece of glass the exact size of the plate. For example, if you are using 5 x 7 plates, use a 5 x 7 glass. You are then ready to make your exposure.