One of the most fascinating of the mechanical arts is working in glass. One reason for this is because it is a substance so beautiful, so hard and so fragile that it seems to the ordinary observer to be beyond the pale of tools.
Au contraire, as the French say it, glass is easily worked if you mix a little skill with the right kind of tools and it gives me much pleasure to tell you how to do it. Further, the tools you need are few and the material is inexpensive.
Before getting down to the processes by which glass can be worked it is a good scheme to know about the substance itself.
Hieroglyphic 88 inscriptions on the Egyptian monuments show that the art of working glass was practiced 4,000 years ago or before the Hebrew exodus.89 Now glass is a chemical compound, the chief substance of which is sand.
Common glass is made by melting sand, lime and soda together. Sand is formed of a chemical element called silica; lime is calcium carbonate and soda is sodium carbonate and there you have three chemical elements which when they are melted together make common window glass.
88 The early Egyptians carved the history of their arts on stone in a sign language called hieroglyphics from the Greek hieros which means sacred, and glypho which means to carve.
89 The departure of the Israelites from Egypt under the guidance of Moses.
Glass which contains lime is called crown glass and it is this kind which is used in making one of a pair of achromatic 90 lenses. Flint glass which is the kind of glass used in making the other one of a pair of achromatic lenses contains lead instead of lime.
Flint, or lead, glass melts more easily than crown, or common, glass and this is a good pointer for you to remember when you are getting glass for your glass blowing experiments. Bohemian glass, which is largely used for chemical apparatus, is made of sand, lime and potash.
Colored glass is made by putting small quantities of various substances into the melted glass. Thus oxide of cobalt91 gives a blue color; oxide of chromium, or cupric oxide a green; one of the copper oxides gives it a red color, uranium 92 a yellow, etc.