Gutta-Percha for Coating Glass.—For focusing glass in photography and for similar purposes where ground glass or a translucent material is required, a solution of gutta-percha in chloroform is highly recommended. This is flowed over or painted on the glass and is allowed to evaporate afterwards.
Burned Rubber.—A very soft pure gum sold for artists’ use is improperly termed burned rubber. It is used in crayon work for removing and lightening marks by dabbing it against the paper, cleaning the rubber from time to time. It is so soft that it picks up and removes crayon marks without the necessity of friction. Thus the rubbing out or more properly erasing operation can be localized and crayon tints can be lightened in tone without impairment or “smutting.” It is a very elegant accessory to the artists’ paraphernalia. To make it, pure virgin gum, preferably the best Para, is cut into pieces and soaked for some hours in benzole. A long soaking is advisable. The pieces are then removed from the benzole and are ground in a mortar until perfectly homogeneous. The mass is gathered up with a spatula and is pressed into little tin boxes. If desired it may be dried upon a water bath. This is not necessary as, if the box is left open, it will rapidly season itself. It should be very soft, should tend to adhere to the fingers, yet should leave them easily, and should strip cleanly from the box. A very little turpentine makes it more adhesive. It may even be softened in turpentine alone. This gives a gum that seasons more slowly and is in some respects preferable to the benzole made preparation. It is sold at a high price by the dealers, as the demand for it is limited.
Rubber Sponge.—This is also an artist’s rubber. It is also used for cleaning kid gloves. It is made by incorporating with the masticated or washed and sheeted gum any material or materials that will give off vapor in the curing process. Damp sawdust and crystallized alum are used as giving off vapor of water or steam, or ammonium carbonate as giving off vapors of ammonia carbonic acid gas and steam. The mixed gum may be cured in moulds, which it will fill by its expansion.
Shellac Varnish for India Rubber.—This is made by soaking powdered shellac in ten times its weight of strong aqua ammonia (26° B.). At first no change beyond a coloring of the solution is perceptible. After many days standing the bottle, which should have a glass stopper, being tightly closed, the shellac disappears, having entered into solution. It may be a month before complete solution. This forms an excellent varnish for india rubber shoes and similar articles. It may be applied with a rag. It is also a good application for leather in some cases and doubtless many other uses could be made of it. It would act well as a vehicle for a dark pigment such as lamp-black. It will rejuvenate a pair of india rubbers very nicely. The ammonia exercises also a good influence on the rubber. It has been recommended as a cement for attaching rubber to metal, but its adhesive powers are not always satisfactory.
Simple Substitute for Stamps.—A very simple though rough and imperfect substitute may be made by gluing with common carpenter’s glue pieces of thick string upon a piece of wood, the string being given the form of the desired letters. Care must be taken to avoid saturating and stiffening the string with the glue.
India Rubber Substitutes.—One of these under the name of vulcanized oil is thus described by Bolas:
“Vulcanized oil is, perhaps, of more interest, and many oils, such as linseed and others resembling it, may be vulcanized by being heated for some time to 150° Centigrade with twelve to twenty per cent. of sulphur. The product obtained is soft, and somewhat resembles very bad india rubber. By increasing the proportion of sulphur very much indeed, say to four times the weight of the oil, and vulcanizing at a higher temperature, a hard substance, resembling inferior vulcanite, is obtained.
“Soft and hard vulcanized oil have been introduced into commerce at various times and under many names; but these materials never seem to have made very much headway.”
Another method of treating the oil consists in mixing it with a solution of chloride of sulphur in carbon disulphide or in naptha. On standing, the volatile solvents escape, leaving a thick mass, which is the substitute.
In combinations of aluminum with the fatty acids, forming aluminum soaps, and of these, aluminum palmitate especially, a substitute for india rubber has been sought but without success.