Dry clay, powdered and sifted as fine as possible, is used for plugging, or stopping up the bottoms of cases. I have, for some time, discontinued its use, and employ plaster of paris in preference. Directions will be given for each, so that the learner can adopt which he pleases: but plaster is infinitely preferable. It is an American improvement.
Roman Candle Scoops.
No species of fireworks require greater care in their construction than roman candles. In the first place the stars must be fierce, that they may light thoroughly: next, they must not be driven out with too great velocity. For this purpose the blowing-powder must be carefully adjusted. The stars, also, must be of so easy a fit that when put into the case they may fall to the proper depth of their own accord. If they require pushing, they are too tight, and will probably be blown out blind. When made as directed they will, necessarily, be of an easy fit, as they will be of the inner diameter of the brass tube, while the bore of the case is equal to its external diameter.
To regulate the blowing powder, prepare a number of little scoops, like fig. 5, which is about the right size for the bottom star. They are formed of pieces of tin, zinc, or copper. Cut a long strip of tin, 1⁄2 an inch broad; cut this across into 7 pieces, of the following lengths, 15⁄8, 16⁄8, 17⁄8, 2, 21⁄8, 23⁄8 and 4 inches. Round off the corners. Take a piece of brass wire, or stair-rod, about 1⁄4 inch diameter, and with the wooden mallet, before mentioned, fig. 26, bend each of the pieces round the rod into a half cylinder, or gutter. Take up the smallest, and hold 5⁄8 of an inch of the end of the stair-rod in the end of the semicylinder, to keep it open; put the other part from a to b, fig. 5, in a vice, and pinch it up; it will assume the form represented; the bowl part will be 5⁄8 long, and the handle 1 inch long. Make the bowl of the next scoop 6⁄8 of an inch long, the next 7⁄8, and so on; the handle will always be 1 inch long. The last, for the top star, will have a bowl of 3 inches. The smallest scoop ought to hold as much grain powder as will weigh about 1⁄12 of the star; but to have the scoops accurate, it will be necessary to charge a roman candle, fire it, and observe whether the stars go a uniform height. For measuring the interval fuse, or fuse between the top of one star and the bottom of the next, a large scoop of the size of fig. 10 will be required. The tin may be an inch broad, and the bowl part 21⁄2 inches long, bent round the rammer, fig. 4. To adjust it, take a roman candle case, fit it on the foot, fig. 9, which is a piece of wood, or brass, turned with a tenon to fit tight in the bottom of the case. Fill the scoop, and strike it level, with a straight-edge; empty it into the case, rest the foot on a flat surface; insert the rammer, fig. 4, and jolt it up and down, a dozen times, or more, lifting it about 1⁄2 an inch at a time; put in another scoopful, and jolt it in like manner. If the 2 scoopfuls, thus compressed, fill an inch of the case, the scoop will be correct. If more or less, the scoop must be shortened, or lengthened, accordingly.
A piece of writing-paper may be pasted and wound twice round the handle of each scoop, as from a to b, fig. 4. One dot can be put upon the scoop, for the first, or bottom, star; two dots, for the second scoop, &c., or any memorandum can be written upon them, for future guidance. Should they get soiled, they may be cleaned with a soaped damp piece of sponge.
Gunpowder, for fireworks, is used in two forms; meal-powder, and grain-powder. Meal-powder is a fine black dust, and is employed in all cases of mixing. Grain-powder is of three kinds, F, FF, and FFF, fine, double fine, and treble fine. FFF is best for crackers, simply because it runs rapidly down the pipes: for driving stars, shells, &c., F will be sufficient; but FFF may be employed: FF need not be purchased. All kinds of powder may be obtained of Pinnell, 214, Whitechapel Road. If, in any place, there should be a difficulty in obtaining meal-powder, F grain-powder may be crushed in a leather bag, by laying the bag on a hard surface, and beating it with a hammer. The leather should be of the same kind as shoes are made of.
To Charge Roman Candle Cases.
Pour some F grain-powder into a wooden bowl, or platter, represented by fig. 11. Round the edge lay the little blowing-powder scoops, side by side, beginning with the smallest at a, the next at b, and so on to g. Put some roman candle fuse into a large tin scoop, made to stand on a flat bottom, like fig. 12, the same, in shape, as used by tea-dealers; and, on the right-hand of it, lay the charging-fuse scoop, fig. 10. If the roman candle is to contain different-coloured stars, set seven in a row, in the order desired. When the cases are intended to be fired in threes or fours, the stars in one may be all blue, in another crimson, in another green, in another white. Fit the foot, fig. 9, in the bottom of the case, put in a scoopful of clay, insert the rammer, fig. 4, and jolt it till the clay is well compressed. The clay should fill 1⁄2 an inch. This being done, invert it, and shake out any little dust that may remain. Put in the little scoopful a, of F grain-powder; then lay the scoop at A. Now put in a star. As previously stated it ought to fall of its own accord; but make sure that it has reached the blowing-powder, by putting in the rammer. Having ascertained this, put in a scoop of fuse, fig. 10; lay the scoop on the left of fig. 12; insert the rammer and jolt it; put in another scoop of fuse, fig. 10; lay the scoop on the right of fig. 12; insert the rammer and jolt it, as before. Then proceed with the scoop b of grain-powder, and lay it at B, and so on, till the case is filled. The fuse on the top star is best driven in with a short solid rammer and mallet, as it is difficult to jolt the long rammer in so small a space. The last 1⁄8 of an inch, near the mouth of the case, should be fine meal-powder, as it binds better than the roman-candle fuse, and also blows off the leader pipe.