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.
Dark Room. The first point to consider in the developing of the dry plate is the room in which you are going to develop, commonly called the dark room. This is somewhat of an erroneous term, as the room must not necessarily be dark, as the term would imply, but only in a chemical sense. By a dark room we mean a room which, when the door is closed, is free from any actinic light. The only light in the room must be produced by the dark room lamp, or window, commonly called the ruby light; a combination of ruby, orange and yellow, which is non-actinic, but only to a certain extent. The dry plate of to-day is more or less affected by all colors. You should, therefore, never place a plate while changing or developing too near your ruby light. You can examine your plate occasionally by holding it up close to the ruby light, but only for a few seconds at a time.
Dark Room Light. Besides the quality, the quantity of light must be considered. You should always employ artificial light, as daylight is apt to vary. If you are not going to use a regular dark room lantern, over your sink you should have a window. In this window place your combination of ruby, yellow and orange glass. On the outside place a shelf for the light. On this you can place your lamp or adjust the gas jet or electric light. This will keep the heat out of the dark room.
Size Of Dark Room. In a professional studio where a large amount of developing is to be done, the dark room should be fairly large. It is a mistake to suppose that a small closet or cupboard will do, as it would be extremely injurious to the health of those who were compelled to remain in such a small room for any length of time. For the amateur who only develops a plate at a time, a small dark room is perfectly safe and practical; but in either case the dark room should be kept perfectly clean and there should be a place for everything and everything in its place.
ii. Ventilation. - In preparing a perfect dark room, ventilation should also be considered. There should be an outlet for foul air at the top of one of the walls. It should be so arranged that the foul air can be let out without letting in light. (See Illustration No. 1.)
Illustration Nos. I and 2 Simple Method of Ventilating a Dark Room See Paragraph No. 11.
Illustration No. 3 Floor Plan of a Convenient Dark Room See Paragraph No. 14.
Illustration No. 4 Sectional View of Convenient Dark Room See Paragraph No. 15.
There should also be an inlet for the fresh air, and this may be provided by piercing a number of holes at the bottom of the door and arranging a hood over them. (See Illustration No. 2.)