Shells that are designed for stars only, may be made quite round, and the thinner they are at the opening the better; for if they are too strong, the stars are apt to break at the bursting of the shell: when you are making the shell, make use of a pair of calibers, or a round gauge, so that you may not lay the paper thicker in one place than another; and also to know when the shell is of a proper thickness; ballóóns must always be made to go easy into the mortars.
The performance of the principal part of fireworks depends much on the compositions being well mixed; therefore great care ought to be taken in this part of the work, particularly in the compositions for sky rockets. When you have four or five pounds of ingredients to mix, which is a sufficient quantity at a time (for a larger proportion will not do so well), first put the different ingredients together, then work them about with your hands, till you think they are pretty well incorporated; after which put them into a lawn sieve with a receiver and top to it; and if, after it is sifted, any remains that will not pass through the sieve, grind it again till fine enough; and if it be twice sifted it will not be amiss; but the compositions for wheels and common works are not so material, nor need not be so fine. But in all fixed works, from which the fire is to play regular, the ingredients must be very fine, and great care taken in mixing them well together; and observe that, in all compositions wherein are steel or iron filings, the hands must not touch, nor will any works, which have iron or steel in their charge, keep long in damp weather, without being properly prepared, according to the directions given in the following article.
It sometimes may happen, that fireworks may be required to be kept a long time, or sent abroad; neither of which could be done with brilliant fires, if made with filings unprepared; for this reason, that the saltpetre being of a damp nature, it causes the iron to rust, the consequence of which is, that when the works are fired, there will appear but very few brilliant sparks, but instead of them a number of red and drossy sparks, and besides, the charge will be so much weakened, that if this should happen to wheels, the fire will hardly be strong enough to force them round: but to prevent such accidents, prepare your filings after the following manner.