Of the Spur-Fire.
This fire is the most beautiful and curious of any yet known, and was invented by the Chinese, but now is in greater perfection in England, than in China; and as it requires a great deal of trouble to make it to perfection, it will be necessary that young beginners should have full instructions in every particular; therefore care ought to be taken that all the ingredients be of the best sort, that the lamp-black is not damp and clodded, and that the saltpetre and brimstone are thoroughly refined. This composition is generally rammed in one or two ounce cases, about five or six inches long, but not drove very hard; and these cases must have their concave stroke struck very smooth, and the choak or vent not quite so large as the usual proportion; this charge, when driven and kept a few months, will be much better than when just rammed, but will not spoil, if kept dry, in many years.
Now as the beauty of this composition cannot be seen at so great a distance as brilliant fire, it has a better effect in a room than in the open air, and may be fired in a chamber without any danger; for it is of so innocent a nature, that, though with an improper phrase, It may be called a cold fire; and so extraordinary is the fire produced from this composition, that, if well made, the sparks will not burn a handkerchief, when held in the midst of them; you may hold them in your hand while burning, with as much safety as a candle; and if you put your hand within a foot of the mouth of the case, you will feel the sparks like drops of rain. When any of these spur-fires are fired singly, they are called artificial flower pots; but some of them placed round a transparent pyramid of paper, and fired in a large room, make a very pretty appearance.
The Composition for the Spur-fire.
Saltpetre four pound eight ounces, sulphur two pound, and lamp-black one pound eight ounces.
Or, saltpetre one pound, sulphur half a pound, and lamp-black four quarts.
As the spur-fire composition is very difficult to mix, and the manner of doing it quite different from any other, I shall here treat of it separately; for example, the saltpetre and the brimstone must be first sifted together, and then put into a marble mortar, and the lamp-black with them, which you work down by degrees, with a wooden pestle, till all the ingredients appear of one colour, which will be something greyish, but very near black; then drive a little into a case for tryal, and fire it in a dark place; and if the sparks, which are called stars, or pinks, come out in clusters, and afterwards spread well without any other sparks, it is a sign of its being good, otherwise not; for if any drossy sparks appear, and the stars not full, it is then not mixed enough; but if the pinks are very small, and soon break, it is a sign that you have rubbed it too much.
N. B. This mixture, when rubbed too much, will be too fierce, and hardly shew any stars at all; and, on the contrary, when not mixed enough, will be too weak, and throw forth an obscure smoke, and lumps of dross, without any stars. The reason of this charge being called the spur-fire, is because the sparks it yields have a great resemblance to the rowel of a spur, from whence it takes it’s name.
Characters, or significant Signs, for distinguishing the different Ingredients used in Fireworks.