Glass is usually brought into shape by being moulded or blown. Simple and complete directions for blowing small articles may be found in the Young Scientist, vol. I, p. 37.
There are a few other operations, however, which are con stantly needed by the amateur and which we will describe.
For ciitting flat glass, such as window-panes, and for cutting rounds or ovals out of flat glass, the diamond is the best tool; and, if the operator has no diamond it will always pay to carry the job to a glazier rather than waste time and make a poor job by other and inferior means. When, however, it is required to cut off a very little from a circle or oval, the diamond is not available, except in verj skilful hands. In this ease a pair of pliers softened by heating, or very dull scissors is the best tool, and the cutting i-best performed under water. A little practice will enable the operator to shape a small round or oval with great rapidity, ease and precision. When bottles or flasks are to be cut, the diamond is still the best tool in skilful hands; but ordinary operators will succeed best with pastils, or a red hot poker with a pointed end. We prefer the latter, as being the most easily obtained and the most efficient; and we have never found any difficulty in cutting off broken flasks so as to make dishes, or to carry a cut spirally round a long bottle so as to cut it into the form of a corkscrew. And, by the way, when so cut, glass exhibits considerable elasticity, and the spiral may be elongated like a ringlet. The process is very simple. The line of the cut should be marked by chalk or by pasting a thin strip of paper alongside of it; then make a file mark to commence the cut; apply the hot iron and a crack will start; and this crack will follow the iron wherever we choose to lead it. In this way jars are easily made out of old bottles, and broken vessels of different kinds may be cut up into new forms. Flat glass may also be cut into the most intricate and elegant forms. The red hot iron is far superior to strings wet with turpentine, friction, etc.
For drilling holes in glass, a common steel drill, well made and well tempered, is the best tool. The steel should be forged at a low temperature, so as to be sure not to burn it, and then tempered as hard as possible in a bath of salt water that has been well boiled. Such a drill will go through glass very rapidly if kept well moistened with turpentine in which some camphor has been dissolved. Dilute sulphuric acid is equally good, if not better. It is stated, that at Berlin, glass castings for pump-barrels, etc., are drilled, planed and bored, like iron ones, and in the same lathes and machines, by the aid of sulphuric acid. A little practice with these different plans will enable the operator to cut and work glass as easily as brass or iron.
Black diamonds are now so easily procured that they are the best tools for turning, planing or boring glass where much work is to be done. With a good diamond a skilful worker can turn a lens roughly out of a piece of flat glass in a few seconds, so that it will be very near the right shape.
A splinter of diamond may be very readily fastened in the end of a piece of stout brass wire so that it may be used for drilling or turning glass. Bore a hole the size of the splinter and so deep that the diamond may be inserted beyond its largest part, but leaving the point projecting. Then, by means of a pair of stout pliers, it is easy to press the end of the brass so that it will fill in around the diamond and hold it tight. Diamonds are sometimes cemented in such holes by means of shellac, or even solder run around them. This answers for some purposes, but not for drilling or turning.