A very good cement for glass (Lehner) is as follows:
| Gutta-percha | 100 |
| Black pitch (asphalt) | 100 |
| Oil of turpentine | 15 |
This is a glue of general application, and specially good for leather and mending shoes.
The reader who would thoroughly study the subject of glass may consult Die Glas-Fabrikation, a very admirable work by Raimund Gerner, glass manufacturer; A. Hartleben, Vienna and Leipzig, price 4s. 6d.
Small triangles of sheet tin or iron are often used to fasten panes.
The mending of broken glass is in most cases much the same as that of broken crockery or porcelain. The cement made from mastic, or mastic combined with sturgeon’s bladder, or generally of silicate with whiting, is the proper adhesive. As silicate of soda is simply liquid glass, it can be employed to fill spaces or to make glass; but, owing to its sticky nature, it is hard to manage. This may be often effected by first preparing a layer of soft paper, on which successive coats of silicate are laid. When dry the paper can be washed away.
Silicate of Soda has become of such importance that a French work on mending fictile ware is almost entirely limited to its use as a binder, when combined with whiting. Water-glass was long supposed to be a modern invention, till some one found it described in Van Helmont’s works, A.D. 1610. But I have found it also in the Joco-seriorum Naturæ, 1545; in the Magia Naturalis of Wolfgang Hildebrand, which is of the same time; and, finally, by Paracelsus (Liber de Præparationibus), where he describes it as Destillatio Crystalli. And the author of the Joco-seriorum speaks of soft glass as a thing which had been treated by several writers.
According to Wagner there are three kinds of soluble glass—(i.) the soluble potash glass, 45 silex, 3 charcoal, 34 carb. potass.; (ii.) soluble soda glass, 100 pts. quartz, 60 cal. sulp. soda, 15 of charcoal; (iii.) double soluble glass, 100 quartz, 22 cal. soda, 28 carb. potass., 6 wood-coal. Water-glass combines well with any “indifferent” powder, such as powdered glass, to make a strong cement. To powder glass, heat it red-hot, drop it into cold water and pulverise it. It will become as fine as flour, and in this state combines with gum-arabic, or glue, or gums to make a powerful glass-mender. Mixed with powdered glass, oxide of zinc, or whiting, powdered marble, calcined bone, plaster of Paris, wood-ashes, &c., it can be worked like putty. Mixed with colours it is used for stereochrome painting, a kind of fresco.
Missing pieces of glass, such as leaves from a chandelier, can be easily replaced with water-glass, and all cracks or defects glazed over with it.
This mending is allied, however, to certain processes in art which are so interesting that I venture on a description of them.