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.
Preparing Apparatus For Artificial Light. Bromide enlargements can be made equally well at night by the use of artificial light, although the necessary exposure will be considerably longer. In this case you can use your regular dark-room. The accompanying Illustration No. 13 will serve to show how to prepare a box for the use of electric light. A good, large box should be used in order to keep the bulb cool, and the hole in the top of the box, through which the electric cord enters, must be protected by a bushing. This can be done by using a 2-inch piece of rubber hose or tubing. Fit this in the top of the box and pass the electric cord through it. A good plan is to also have a small door in the back of the box, through which you can turn the light on and off. To make this box absolutely fire-proof and safe, line it with asbestos, more especially if it is rather small. If it is a fair sized box, line it with tin and it will be perfectly safe, while the tin will act as a reflector and increase the strength of light. The front of the box should be fitted with a sheet of ground-glass. Set the box on a table and then place the camera in front of the ground-glass, exactly the same as when using the window.
607. In case your dark-room is very small and you have no electric light but must use some other artificial light (lamp light for example), then prepare your darkroom so that you can place your lamp on the outside of the door or one of the walls, about three feet from the floor, with an opening cut in the wall large enough to receive the ground-glass or negative space of your camera. Build a shelf both on the inside and outside of this opening, the one on the inside to hold the camera and the one on the outside to hold the box containing the artificial light.
608. The box containing the light must be lined with either asbestos or tin. This lining will answer three purposes-it concentrates the light, acts as a reflector, and also makes the box fire-proof. A ground-glass must be fitted in the one side facing the dark-room. If it is possible, use an opal glass in place of ground-glass. This is a milk-white glass, with which, you will find, you will produce a whiter and more evenly distributed light. This ground-glass or opal glass is to take the place of a condenser and if your light is placed far enough away from the ground-glass it will diffuse evenly. The correct distance between the light and the ground-glass is twice the diagonal of the negative employed. This extra ground-glass is not necessary when using the ground-glass which is on the camera.
609. Any kind of light can be used. If electric light can be had then drop two 32 candle-power incandescent lights into the box, one in each corner and some little distance to the rear so as to bring the lights away from the ground-glass as far as possible. If no electric light can be had, two gas jets or two kerosene lamps will do. If the latter are used it is necessary that there be two openings at the top of the box to give draught to the chimney. A low lamp is best as the flame will be centered more evenly.
610. Where electric light is used and the dark-room is sufficiently large, there will be no necessity of cutting a hole in the wall and placing the light on the outside, as the box containing the electric light can be made entirely light-tight and can be used inside of the dark-room. If gas or kerosene light is used you could not close the box entirely as both must have some air to burn well and give white light.
611. When using kerosene we would advise placing a piece of camphor, about the size of a walnut, into the oil.
Illustration No. 14 Condensing Lens See Paragraph No. 612.
This camphor will cause the oil, when burning, to give a whiter-more actinic-light.