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 The Fuse. To prepare the fuse, where a flat pan is used, place a little cotton batting or absorbent cotton on the pan (a pan with a handle preferred), pour sufficient powder on the cotton, well scattered, and allow a small piece of the cotton to hang over the edge of the pan, say four inches. Use this as a fuse for igniting and setting off the flashlight. When you are all ready place the pan on a table, or step-ladder, and light the end of the cotton with a match or lighted candle. Do not look into the flash, but as soon as you light the cotton turn your face away from the powder, as the light is very dazzling and not good for the eyes.
Placing The Flashlight. The proper location of your light depends a great deal on what you are photographing. If you are making a picture of an interior of a room, you should place the flash one foot higher than the top of the camera and only a trifle to the side of it. This will save heavy shadows against the wall or background which would result if the flashlight were placed more to one side. If you are making a group picture you should turn the faces a trifle away from the light and where a muslin screen can be used between the flash and the group, it will be better to locate the flash more to the side. (See the following chapter - Flashlight Portraiture.) For general interior work it is best to place the lamp close to the camera.
483. Shielding the Lens. Caution. - When arranging the flash-machine, see that it is placed in such a position as not to reflect into the lens, as the plate would be instantly fogged and your negative result in a failure. Where you find it necessary, which may be the case when working in close quarters, to place the flash in front of the line of the lens, carefully shield the flash from the lens by means of a screen or cardboard placed between the lens and the flash. Another caution is, never, on any account, use flashlight compounds in a magnesium lamp or cup intended for pure magnesium powder, for, in doing so, you are sure to have an explosion.
Practice Work. For your first experience at flashlight photography, you should not attempt to work with difficult subjects, such as portrait or group subjects. Try an interior or a still-life object - a vase, a small piece of carving or statuary, etc. In so doing you will become acquainted with the manipulation of the powder and be better able to judge more accurately how much powder is required and how to control the light on the object. With the object about four feet from the lens and your flashlight placed to one side of the camera, you will require, if the flash-sheets are used, about eight to ten inches of the flash-sheet, or about twenty grains of flash powder. With this amount of illumination and with the lens stopped to f. 8, using ordinary dry plates or film, you should be able to make a fully timed exposure.
Developing. The plate should be developed with a quick-acting developer, such as Pyro, Metol, Rodinal, etc. The Universal Pyro formula given in Vol. II will give good results. Strive for delicacy of detail; avoid contrast and density. It is advisable always to cover the tray during development. Make proof prints of all exposures. Note on the backs of these proofs all data connected with the producing of the results, whether by flash-sheets or flash-powder, giving number of the negative, subject, date, etc. Also give the distance (in feet) of subject from lens and background; distance of the flash to right, left, front or back, or above subject and amount of flash-powder used; kind of reflector, aperture of lens, plate used, etc. Each and every one of these items are useful for your future guidance.