Pyrotechny, the art of making fireworks, is of unknown antiquity. It was practised amongst the Chinese from very early times, and has attained with them so much perfection that the beauty and ingenuity of their devices have often been admired by Europeans. Fireworks, as the name is now understood, were hardly known in Europe until the nature of gunpowder became known, and for a long time only very simple pyrotechnic contrivances were used.
The compositions employed for most kinds of fireworks are of the nature of gunpowder. That is to say, the mixtures of which they are made contain combustible or oxidisable substances, along with bodies available for their rapid combustion, since these latter contain large quantities of oxygen. The most frequently employed combustible materials are carbon (charcoal) or some compound of carbon, such as sugar or gum, and sulphur or a compound of this element, such as sulphide of antimony. Such bodies as charcoal and sulphur burn slowly in common air, because its oxygen is largely mixed with nitrogen, which does not support combustion; but when they are compounded with nitrates and chlorates the store of oxygen in these salts being given off by heat enables the firework composition to burn at a more or less rapid rate whenever a spark is applied to it. It is not desirable, however, to have too sudden a union of combustible matter with oxygen, hence violent explosives, like nitro-glycerine, are unsuitable for showing coloured or brilliant flames. The two most important oxidising ingredients used in firework compositions are nitrate and chlorate of potash. Iron, in the form of cast-iron or steel, and in a state of fine division, is a frequent ingredient in fireworks, and to some extent the powder or filings of antimony, zinc, magnesium, and copper are also employed. When the particles of these metals are highly heated they produce sparks and scintillations of different colours. A few substances, such as sand and sulphate of potash, are used to modify the rate of combustion.
Variety of colour is much studied in the production of fireworks, as it contributes greatly to their beauty. The colours usually seen are those given by simple metals when burned. Compounds of the metals form part of the mixtures, and these are reduced to the metallic condition in a state of very fine division by contact with the carbon present in the hot mass. A yellow colour is one of the most easily managed, any of the common compounds of sodium producing it. Copper gives a green colour when burned in a hydrogen flame, which changes to blue in the presence of a little free chlorine; so that when this metal is used for green some substance containing hydrogen is added, and when employed for blue, calomel (one of the chlorides of mercury) is put into the mixture. Nitrate of barium is also employed for green. Salts of strontium give fine crimson tints, calcium compounds a red, and lithium carbonate (a costly substance) a purple red. Among the substances used to produce white colours are sulphide of antimony and sulphide of arsenic.
The cases which contain the firework compositions are carefully made of paper or pasteboard, or both, pasted in layers. They are usually cylindrical in shape, and the proportion of length to diameter, and the size of openings for the escape of the burning mixtures, are matters of importance. So also is the proper mechanical construction of the framework of rotary fireworks. Touch-paper, prepared with a solution of nitrate of potash in alcohol, is used for capping squibs, crackers, and indeed for all kinds of fireworks; quick-match of cotton-wick, which has been saturated with gunpowder, gum, and other ingredients, connects the parts of complicated designs; and portfires, small pencil-like articles filled with saltpetre, sulphur, and gunpowder, are used to fire the touch-paper cappings.
The simpler kinds of fireworks include squibs, crackers, gerbs, Roman candles, stars, sparks, maroons, theatre-fires, Bengal lights, &c. Squibs are small stout paper tubes filled with grained powder, to which a little charcoal, sulphur, and steel filings are sometimes added, a sufficient quantity of bursting powder being put in to cause a slight explosion at the end when fired. Crackers consist of a tube bent into folds, and containing meal-powder, charcoal, sulphur, saltpetre, and sometimes iron filings in varying proportions. The folds are tied by a cord; and on a cracker being fired a report is given at every turn of the tube. Serpents are tubes, some of which have a choke in the middle. When fired they take a vizzag direction, and give out a hissing noise. Gerbs consist of a straight cylindrical case filled with a composition which produces a bright sparkling jet of fire somewhat in the form of a waterspout. They sometimes contain coloured stars. Roman candles have a resemblance to gerbs. In filling them stars are placed at intervals along the tube between layers of the composition. Stars are of different kinds, such as simple stars, tailed stars, and pointed stars. Simple stars consist of saltpetre, sulphur, and fine gunpowder made into a paste ball with gum and spirits of wine, and dried.
Sometimes they contain iron filings. Many compositions are, however, used for stars, their various colours alone necessitating this. Sparks, or small stars, are also made of different colours. Maroons are small boxes, round or square, bound with a cord, and containing a composition which explodes with a loud report. Bengal lights consist of compositions varying according to colour, which are burned in small sancers: for example, a red light can be produced by a mixture of chlorate of potash, nitrate of strontia, sulphur, and lampblack; and a green by chlorate of potash, nitrate of baryta, chloride of lead, sulphur, and resin. Theatre-fires are produced by slow-burning compositions containing some colouring ingredient. They are burned without cases on a fireproof slab; and all substances obnoxious when burned indoors, such as sulphur, antimony, and arsenic, or their compounds, should be omitted in preparing them. Magnesium powder and the minute spores of one or more species of lycopodium are used to imitate lightning in theatres.
The most complicated kind of fireworks are some of the rotating wheels. These are called wheels because they have a framework of nave and spokes, round the rim of which cases of the nature of rockets are arranged. They revolve on a pin or metal spindle, and the motion is produced, as will be presently explained, by the recoil as the fire escapes from the cases, which are connected with each other by leaders. There are a number of different forms, but they may be classed under three kinds—vertical, horizontal, and spiral wheels. In the case of the last, a rod (nave) rises vertically from the centre of the horizontal wheel, forming the base, and upon this rod cases are arranged so as to form a spiral. Pin or Catherine wheels and pastilles consist each of a long paper case coiled round a rod in the form of a flat spiral, the case being, of course, filled with a burning composition. Suns are either fixed or revolving. Fixed suns are of various designs, but a common kind has a number of cases radiating from a centre, from which jets of fire proceed outwards. By a suitable arrangement the fire is communicated at the same time to the mouths of each of the cases. Revolving suns are somewhat similar to fire-wheels with spokes. Of ascending fireworks the rocket is the most familiar, and it has been known from an early period. It consists of two parts—viz. a long stick to guide it in its course, and a head. The latter, of strong paper and cylindrical in shape, has its lower portion formed into a hollow cone, base downwards, and round this cone is the burning composition. The object of the cavity is to effect a rapid combustion, which fills it with heated gases, and these, issuing downwards through a small hole in the base, force the rocket up through the air. The upper portion of the head is separated from the lower by a perforated plug of plaster of Paris, through which a fuse passes, so that when the lower portion is burned, the upper, which has a conical head, takes fire and sets off its garniture of stars, snakes, and other ornaments. When fire-arms are discharged there is a recoil, in the case of a heavy gun, of a short distance; in the case of a light cannon, with a larger charge in proportion to its weight, of a much greater distance; and in the case of a rocket which has a bulky charge in a very light barrel the recoil is great enough to send it high in the air. The motion of a fire-wheel is explained in the same way, there being a recoil caused by the backward pressure of the heated gases on the atmosphere as each case on the ring of the wheel takes fire. The tourbillon ascends and rotates at the same time. Upward motion is given by the fire escaping from holes on the under side of the cylinder, and rotatory motion by its finding vent from holes at the ends, but on opposite sides.
Aquatic fireworks, in which the devices which come in contact with the water require to be protected with grease or oil, consist of skimmers or water-devils, floating Chinese trees, gerbs, and Roman candles, water-mines, water fire-fountains, &c. Among recent novelties in pyrotechny are firework-pictures of battles, reviews, and other scenes. Of these perhaps the most popular is the enlargement, in lines of fire, of the portrait of an eminent person in whose honour some public gathering has taken place. The displays of fireworks on some occasions of national rejoicings in Great Britain have cost sums approaching or exceeding £30,000. The greatest displays of comparatively recent date have taken place during the visits of foreign sovereigns to the country. See also LIFE-SAVING APPARATUS, ROCKET, SIGNALS; and T. Kentish, The Pyrotechnist's Treasury: Art of making Fireworks (2d ed. 1887).