Plain magnesium may also be fired with a lighted match or taper if spread on gun cotton, but the flash is not so quick or brilliant as with the mixture.
Flashlight mixtures and powders should be handled with great caution, as they are frequently explosive if treated roughly. The following commercial flash mixtures can be recommended : - " Argen-torat," " Agfa " flash powder, " Ideal " flash powder and Bayer flashlights.
The best home-made flashlight mixture is made as follows : - Sift magnesium powder (3 parts) on a sheet of paper ; and powder potass, chlorate (6 parts), and antimony sulphide (1 part) separately to the finest powder. Mix all with a feather or the dry finger, or shake together in a cardboard box. Seven grs. burn in from 1/20 to 1/40 sec. Each ingredient should be perfectly dry. Never use a flash mixture in a reservoir lamp - only plain magnesium.
THE EXACT AMOUNT OF FLASHLIGHT necessary for producing perfect results depends upon four conditions - the speed of the lens, the colour of the object photographed and the surroundings, the speed of the plate and the distance of the light from the sitter. The following will be found a guide when a rapid plate, say, 200 Watkins, is used ; the lens working at f/8, the sitter wearing moderately light clothes, and the walls of the room not being very dark. At a distance of 5 feet from the head of the sitter use 12 grains of flashlight mixture. At a distance of 10 feet use 30 grains. At 15 feet use 70 grains and at 20 feet use 100 grains.
PLATES. It is advisable under all circumstances to employ rapid plates for flashlight work. In fact, the more rapid they are the better, if soft results are desired. They should be backed to avoid any chance of halation from white collars or drapery, etc., and ortho-chromatic plates possess advantages if the subject has a pronounced colour or freckles, although the use of a colour screen is rather out of the question for the average worker of flashlight portraiture. If ultra rapid plates are used it is possible to cut down the amount of flash powder or use a smaller stop in the lens.
THE POSITION OF THE LIGHT is always a difficult question, but it may be taken as a general rule that an angle of 45° should be followed as regards height and distance from the sitter, while the position of the light in front or behind depends on the type of portrait required. An imaginary square should be drawn thus (Fig. 1): - The head of the sitter should occupy a bottom corner. The best average lighting will be obtained by the light being placed anywhere on the diagonal drawn from the head at the opposite corner. It should be borne in mind, however, that the nearer the light is to the sitter the harsher the shadows will be, while the further off it is - provided the quantity of powder is increased proportionately - the greater the possibilities will be for diffusing it.
THE COLOURS OF THE WALLS and decorations in a room, also the colour of the dress of the sitter have a bearing on the quantity of flash powder necessary, and it is advisable to double the powder in case dark colours prevail. Before fixing upon the position of the light when making a flashlight portrait it is a good plan to use a portable light, such as a good oil lamp, and study the sitter under different conditions of lighting.
All other lights should be turned down in the room and the effect produced on the sitter when viewed from the standpoint of the lens by placing the lamp at different points will be approximately that produced by the flashlight.
A little higher or lower will make a great deal of difference with some portraits. In case of deepset eyes or hollow cheeks, do not place the light too high, but in taking a group it is desirable to have the light as high as possible, so that any shadows cast by one person will not fall on the next.
In any case the position of the light should be such that the effect will resemble as closely as possible the lighting from a studio skylight, and the little diagram given (Fig. 1) indicates roughly what this angle should be.
THE RELATIVE POSITIONS of sitter, flashlight and camera are indicated in the following diagrams. Figure 2 shows a good arrangement for the production of a pleasingly lit portrait with a single flash lamp or one ignition of flash powder on a tray ; 1 is the camera ; 2, the sitter ; 3, the background, if one is used (placed about 4 feet behind the sitter) ; 4, the flashlight (8 feet above the floor, if possible) ; 5, a small screen placed to prevent direct light entering the lens from the lamp ; 6, a reflector to lighten the shadow side of the face, e.g., a piece of white card or paper, or a sheet thrown over a clothes horse or other convenient holder. If flash powder is used, a tin tray or lid of biscuit box forms a good receptacle and a gun cotton train should be spread from side to side. A high pair of steps will answer as a support for the tray, and if a little of the gun cotton protrudes over the edge this can be ignited with a lighted taper when all is ready. Care should be taken, however, not to put the flashlight too near the ceiling.