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.
Backed Plates. The backing of ordinary dry plates is one of the most suitable methods to employ to overcome halation where non-halation plates cannot be obtained. This backing must be in optical contact with the glass; it must have the same "refractive index" as the glass in order to stop reflections from the back; it should contain nothing injurious to the sensitive film; it must not scratch or chip easily, as this would cause dust, which would leave pin-holes in the negative; it should be easily applied and of quick drying quality; it should, also, permit of being readily removed. Backed plates can be purchased ready for use, or can be backed at home. The following formula produces an excellent backing, which can be applied with a brush:
Mix, and then add 2 ozs. of alcohol.
Applying Mixture. Apply the backing to the glass side of the plate, using an ordinary bristle paint brush for the purpose. Of course this must be done in the darkroom. A good way to perform the work is to lay the sensitized plate on a dark card. Fit narrow strips of cardboard (no thicker than the plate) around three edges of the plate. Allow for a slight play, so the plates will not fit too lightly. Glue these strips fast. Whenever it is desired to coat plates, place them in this form, face side down, and paint over the glass. The strips will keep the plate from moving about. This backing will dry quickly and is easily removed.
Black Paper Backing. Another very simple method, which may be used, is to cut the ordinary black paper, in which the plates are packed, the least bit smaller than the size of the plate being used. After cutting, spread glycerine evenly over one side of the paper, and then carefully squeegee it to the back of the plate. The glycerine will hold the black paper in place for a number of weeks, and by simply wetting it is easily removed. Care should be exercised that none of the glycerine gets on the film, or front of the plate. The same form may be used for holding the plate as recommended when painting the plate.
Focusing. In photographing small rooms or well lighted interiors no trouble will be experienced, but sometimes where a large or dimly lighted place is to be photographed, and especially when a wide-angle lens is being employed, it is not so easy to secure a sharp focus on all parts of the room. When the front or foreground of the view is sharp, the distance, in the rear of the room, will be found to be quite a little out of focus. The focus should then be equalized by giving attention to the middle. Select a point between the middle of the view and the foreground and focus sharply on this point. Do this with the open lens, using no stop. This will throw the near foreground slightly out of focus, nearer the middle will be sharp, but the distance may be still out of focus. Then, stop down until the foreground is sharp, when the rear will be sufficiently sharp for all purposes.