CHAPTER VII

FIREWORK COMPOSITIONS

It may have been remarked in the foregoing chapters that, although the ingredients composing the firework mixtures are given, generally the proportions are not.

The reason for this is two-fold: primarily, as we have seen in the chapter on rockets, the proportion of the ingredients of a firework varies in accordance with its size. So that to give the proportions of the compositions of any one type of firework would often require as many formulæ as there are sizes.

Secondly, and perhaps more importantly, the quality and purity of chemicals as supplied in bulk vary so enormously that a constant series of experiments has to be conducted in order to ascertain what modifications and adjustments are necessary in the formulæ to give the required standard of performance.

It is not meant to suggest that the impurities generally to be found in bulk supplies are necessarily harmful to pyrotechnic results. This is not so; salts give far better results in their natural or mineral form than do those prepared synthetically. As an example of this saltpetre may be cited. For pyrotechnic purposes the best obtainable is that from Bengal, yet an analysis of this would probably be found to be less pure than that synthetically prepared in Germany. But experiments have shown that samples of the latter, taken from the same cask, but in different parts, produce very distinctly varying results pyrotechnically.

Pyrotechny is an art, chemistry is a science, and although it is impossible to deny that the former is greatly indebted to the latter for the supply and production on a commercial scale of chemical ingredients, yet it is possible to overestimate the position of chemistry in the art, or possibly it might be more correct to say that pyrotechny has its own chemistry.

Chemistry without pyrotechnic experience is apt to lead to erroneous conclusions. To take a concrete instance: in an article in a famous encyclopædia, obviously written by a chemist of standing, a portion deals with the use of metal salts in the production of colour; the writer gives copper as producing green, which no doubt it does in the laboratory; in practice, however, copper is used solely for the production of blue.

The question of purity in chemicals used in pyrotechny is a secondary consideration, that is, of course, as long as the adulterants have no adverse effect either as regards the pyrotechnic result or the safety of the worker in manipulation. What is of first importance is its pyrotechnic suitability, that is, it must produce the required result and must be consistent. Unequal results are the bugbear of the firework makers. As we have seen, constant experiments are necessary to keep an even standard, but with irregularly functioning chemicals these would be multiplied to an impossible degree.

The first group of compositions for consideration is that nearest related to gunpowder, in fact, for the purposes of a work on pyrotechny, gunpowder may be considered a particular case of this class.

The governing principle of this group, and one may say of all firework compositions, is the same. For combustion to take place oxygen must be present. When an inflammable article such as a piece of paper is set on fire it takes up oxygen from the air. A pyrotechnic composition, however, is so arranged that one of the ingredients has a supply of oxygen which it is ready to give up; another, or others, are of a kind ready to receive and combine with this oxygen.

The oxygen-supplying ingredient which is by far the most frequently used is saltpetre, or, as it was formerly called, nitre, known chemically as nitrate of potash.

Saltpetre may be said to be the basis of pyrotechny. There is hardly a formula by any of the writers on pyrotechny up to at least the middle of the nineteenth century which does not contain it.

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.

Frézier, with more perception than most of the others, realised the shortcomings of such compositions, merely designating them greenish (_verdâtre_), yellowish, reddish, and russet. The only colour which he professes to produce distinct is blue, which he obtained with pure sulphur.

Progress from the earliest times of pyrotechny up to the first quarter of the nineteenth century was very gradual and very slight. The chemicals used by Bate and Babington in their actual pyrotechnic compositions were as follows:—Gunpowder and its constituents, camphor, pitch, resin, orpiment, linseed oil, both pure and boiled, oil of spike (_spica lavandula_), oil of petre (rock oil), an oil known either as benedict or tile, varnish (probably amber), iron scales, and aqua vitæ (spirits of wine).

Bate extends this list considerably by the ingredients of a series of compositions which he has evidently taken from some alchemistic work. These compositions are all either designed to burn under water or to ignite spontaneously in water, and fall somewhat outside the bounds of our subject. Frézier also includes these, evidently from the same source.

Bate also refers to a liquid, the recipe for which was probably taken from the same work.

“Aqua ardens.” The following are his directions for preparing it: “Take old red wine, put it into a glassed vessell, and put into it of orpiment one pound, quicke sulphur halfe a pound, quicke lime a quarter of a pound; mingle them very well, and afterwards distill them in a rosewater still; a cloth being wet in this water will burne like a candle and will not be quenched with water.”

It is difficult to see what he obtained by this process differing from spirits of wine. The quicklime would serve to dehydrate the wine, and probably no part of the orpiment or sulphur would be taken over in the distillation.

Rather over a century later we find Frézier and Jones have made some additions to the ingredients of pyrotechny, the most notable innovations being the use of iron filings (not to be confused with the iron scales of Bate, which were probably hammerslag, the magnetic oxide of iron), steel filings and pulverised cast-iron. Beyond these, and the spark-producing agent already mentioned, the other additions are of small importance, the most notable being lapis caliminaris, or the mineral carbonate of zinc, which however was not used as are metal salts to-day, that is, for the production of colour.

Jones’s book, written some years after that of Frézier, shows little advance from the latter as far as pyrotechnic results are concerned. What he has done, however, is to eliminate what might be called the alchemistic, or one might almost say magic element with which it is pervaded.

In attempting to classify the compositions in Frézier’s book one is staggered by the grotesque character of many of them and by the extraordinary variations in the proportion of their ingredients, even amongst compositions designed for a similar effect.

Presumably with the intention of impressing his readers with the wonders of the science, he added ingredient after ingredient, which, if they did actually no harm to the composition, certainly in no degree assisted its functioning.

In what he calls a simple star there are eleven ingredients, of which, in fact, four only are essential.

Further, beyond the multiplication of unnecessary ingredients in individual compositions, there is often their incompatibility and innate unsuitability for the purpose. Such components as ink, onion juice, and the drainings of a dung-heap suggest so strangely the formulæ of the alchemists that one almost expects to come across “the hair of a Barbary ape,” or similar absurdity.

Ruggieri, who may be considered as the last of the old school, is the first author to deal with the subject in such a way as to convince the professional reader of the practical knowledge of the subject.

His additions to the list of ingredients are not many, but they are genuine. He is the first writer to make use of metals or their salts in the production of colour; he includes among his chemicals metallic copper and zinc, also the acetate and sulphate of copper, and chloride of ammonium. The notable advance in his colour compositions, besides the use of metal salts for that purpose, is the introduction of a chloride, which has the effect of improving the colour by assisting in the volatilisation of the metal. For this purpose he used sal-ammoniac, the use of which has now been almost discontinued on account of its hygroscopic nature, notwithstanding that its base of ammonium is very useful in compositions containing copper. Its place is now generally taken by calomel; in such compositions chloride of sodium had been used for many years, but not as a chlorine carried. Ruggieri appears to have been the first to produce colour on anything approaching modern lines, and although he did not progress greatly, what he did achieve was undoubtedly a marked advance in the art.

His account of the invention of this composition is interesting. He says that he was told by a returned traveller from Russia of a set piece representing a palm tree, “the colour of which rivalled nature.” This piece he set out to imitate, which he did, at any rate to his own satisfaction. The result he obtained would undoubtedly give a good colour, if the method of firing was very clumsy. He remarks that he does not know if his method was as that adopted in Russia, and later of the “merit if not of discovering a new fire at least to have imitated or rather to have rediscovered it.” It appears, therefore, that there may be some doubt as to the originality or priority of Ruggieri’s achievement in this direction, but he must be credited at least with independently arriving at the result. Indeed it is more than probable that the piece seen in Russia was quite different, a transparency or illumination, either imported or copied from the work of Eastern pyrotechnists, and that the whole credit of introducing colour into the art belongs to Ruggieri and to him only.

He mentions that he puts it on record with the object of “thus preventing writers from attributing it to the Chinese, the Medes, or Arabs, as is the custom in Europe, and above all in France, where more than elsewhere there is a mania for enriching foreigners with our merits and to rob ourselves of the birthrights of genius.”