Gunpowder is composed of saltpetre, sulphur, and charcoal, three chemicals which it will have been gathered from the previous pages play a prominent part in very many of the pyrotechnic compositions. In some compositions their proportion is apparently identical with that of gunpowder, yet they do not form gunpowder as they are not milled, and are consequently not so intimately mixed. Compositions containing these ingredients have frequently an admixture of mealed gunpowder, the function of which is to give additional fierceness when required, as is the case in some rocket mixings.
These chemicals, as we have seen in the previous chapters, are the components of rockets, turning cases, tourbillions, saxons, Roman candle fuse, and many others. When variation was required in fireworks used to give a simple fountain effect the earliest addition was of metal in finely divided particles, as filings, borings, or the now almost obsolete iron sand.
Steel filings were used in what was known as “brilliant fire,” a term which has fallen into disuse since the introduction of other metals whose effects eclipsed that of steel. It has also been used where extra effect is wanted, that is, more tail in rockets and tourbillions. It is, however, not much used in the former case to-day, as the presence of steel in a composition which is to be charged on a steel spindle introduces a decided element of risk into the operation.
The introduction of steel and iron was the first use of metals in firework making, probably the next metal to be introduced was antimony, either black (sulphide) or regulus. Jones (1765) was already using what he calls crude antimony; this was probably the black sulphide.
Before the introduction of genuine colour, and while the chemicals which had been adopted for pyrotechny were still very limited in number, attempts were made to obtain either a semblance of colour or some variety in stars and garnitures by the addition of such substances as powdered glass, brass, sawdust, beech raspings, which appear to have functioned as do the iron or steel in the compositions already discussed, except that there would be no coruscation even with the brass. These additions would merely show as red-hot particles in the jet of fire.
Kentish gives two gerb compositions, one of which contains coke grains, and the other porcelain grains, which would apparently produce cognate results; the use, however, of both these ingredients is now almost if not quite obsolete.
Antimony, on account of its ready combustion, is more completely consumed before leaving the case. In this connection it may be mentioned that care is necessary in a mixture containing steel or iron to avoid too large a proportion of the oxygen-bearing ingredient, for fear of consuming it inside the case.
Another composition producing remarkable coruscations is the old-fashioned “spur fire,” which consists of saltpetre, sulphur, and lampblack. This composition requires very careful and experienced mixing, or no effect will be produced, rendering its preparation a very lengthy process.
This difficulty was somewhat overcome during the last century by the addition of orpiment or sulphide of arsenic. Even with this addition, however, its manufacture requires care and patience. It is a curious fact that this composition, unlike most others, has the quality of markedly improving by keeping. How the lampblack produces this unique effect, or why its effect should be so different from that produced by any other form of carbon, has not been satisfactorily explained.
The compositions we have been considering fall into one of two classes, namely, those to produce force and those to produce sparks. These two classes, with one other, namely that of colour, may be said to include all the modern recreative firework compositions. Up to the end of the eighteenth century the ingredients used in the production of the compositions of these three classes were very few in number. A considerably larger number went to supply the ingredients for a fourth class now almost extinct, these might be called the flame-producing class. The principle on which these compositions were designed was, as it were, to overload a mixture of saltpetre and sulphur with combustible material; this latter took the form of gums, resins, or fats, the object being to produce a reddish or golden coloured flame. The early writers give formulæ for variously coloured stars and fires, which must have required considerable effort on the part of the observer for identification. These belonged to the flame class.