Almost any kind of wood charcoal may be used in pyro-techny, and there is ordinarily little difference in the effects produced by the different sorts. There is, however, some variation in color which is due to the nature of the wood used. Thus, for example, oak gives a flame somewhat redder than that caused by other woods. The artificers prefer for charcoal a wood that is both soft and light, such as willow. It is to be noted that soft woods produce a charcoal that is correspondingly light, and that this wood gives a much larger volume than a harder, heavier wood, even when the weight of the two woods is equal. The proportion of soft wood to hard, as regards the production of charcoal, is about 9 to 6. In France, basswood is commonly preferred.
Wood that is to serve this purpose should be very dry and stripped of its bark. It- is burned in the fireplace or else-where, and, as embers are formed, they are shut within a vessel. When these are extinguished the attached cinders are removed and placed in a sieve until they become wholly black.
The mixture of charcoal and sulphur, which should give additional force to the saltpeter, is not quite the same for fireworks as for other uses. Less of the mixture is required for fireworks. The crushing for gunpowder separates the charcoal and sulphur into particles smaller than those of the composition used in fireworks, in which there is a large surface to the grains.
For the mixture of the composition to be used in rockets and other fireworks, the greatest force is given by charcoal alone, without sulphur. Six ounces of charcoal from hard wood, or a full 5 ounces from soft wood, are added to 1 pound of saltpeter. This proportion is based on an average size for the grains. Should these be either larger or smaller, a corresponding increase or diminution of the quantity is required.
Sulphur added to this mixture increases the force up to the quantity of 2 ounces. But this increase will be greater if, when adding the 2 ounces of sulphur, the quantity of hard-wood charcoal is reduced from 5 ounces to 6 ounces. By this mixture of 5 ounces of charcoal from hard wood and 2 ounces of sulphur to the pound of saltpeter, the greatest force is obtained for the powder.