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.
677. Frequently it is desired to make a photograph of an improperly lighted interior. The problem, then, is to secure even illumination and, at the same time, procure detail in the deepest shadows of certain portions. Perhaps there will be but one window in the room, and you might wish to point the camera directly toward it in order to photograph certain objects in that particular part of the room. It would, of course, be necessary, if using daylight, to have the curtains raised and allow the light to enter here. But for average work it would be almost impossible to secure proper results by pointing the camera directly towards the source of light. There may be other difficulties besides, which would not permit you to secure the desired results by using daylight as your illuminant. In such cases you can resort to artificial light. The best and most convenient to employ is flashlight. There are many methods of using this artificial light, the two ordinarly employed being flash-powder and flash-sheets.
678. For many purposes flashlight is more desirable than sunlight. If properly handled it can always be depended upon to give illumination when wanted. With it you will be able to secure just the right amount of brilliancy. It can also be so placed that the shadows will fall in the desired direction. To the amateur worker especially, flash-345 light photography is a special convenience, and as photographic work is frequently confined to the night, he should by all means understand its use.
679. It is frequently desirable to photograph a large room which is illuminated by only one small source of light. Again, to secure a full time exposure in the darkest corner of the room would cause a decided over-exposure near the window. The flash-powder may be placed in such a position that it will illuminate this dark corner, being so concealed by some article of furniture or a screen, that it does not strike the lens. These ordinary uses of the flashlight will enable any amateur to secure successful results; in fact be equal, if not superior, to the ordinary snap-shots out of doors.
Flash-Powder. Flash-powder is put up in various ways - it is usually supplied in one ounce bottles or boxes. Perhaps the most popular brands of flash-powder (yet all are good) are the Luxo, the Nichols, the Victor and the Eastman. The latter company also put up what is known as flashlight cartridges, which have a fuse attached to the cartridge for igniting them. Each cartridge contains a certain amount of powder. When a large flash is required, more than one cartridge may be employed. They also supply what is known as flash-sheets, which are used by simply pinning them up against a cardboard on the wall and igniting the lower corner. (See Paragraph 685.)
Caution. Flash-powder is just exactly as dangerous to handle as gun-powder. It must be kept away from heat. Friction will sometimes ignite it; therefore, be very careful in handling it. Flash-powder must never be used in a magnesium lamp, for with this lamp the magnesium is stored in a chamber and, through a rubber tube, blown into the flame. If flash-powder were used in this machine you would have an explosion. We give these cautions so that you will not meet with accident, yet there is practically no danger if these precautions are observed.