This section is from the book "The Manufacture Of Boots And Shoes: Being A Modern Treatise Of All The Processes Of Making And Manufacturing Footgear", by F. Y. Golding. Also available from Amazon: The Manufacture Of Boots And Shoes.
The success of an adhesive used to unite two substances depends upon the manner of using quite as much as the pasty substance itself. Paste dries by evaporation, and therefore as little as possible should be used. The tenacity of an adhesive depends upon its intimate contact with the surfaces to be united. The chief obstacles to this are dirt and air. Air may be removed by rubbing the paste well into the surface and hammering. Sufficient time must be allowed for drying before stitching.
Paste is the term used to signify the homogeneous mass made by mixing the flour of cereals with water. Most of the farinaceous ingredients thus used consist of two substances, starch and gluten. Starch is insoluble in cold water, but when covered with boiling water the starch-cells swell, forming a glutinous mass. Gluten is a sticky, tenacious, brown mass, very liable to speedy decomposition. It is more adhesive than starch, although less durable. Starchy materials should be mixed to a smooth paste, boiling water being added, and the mass quickly stirred. To starchy pastes it is advisable to add glue, to increase the adhesiveness and stiffness. Preservatives are to be added to prevent decomposition.* Rye flour is rich in gluten, and is cheap. It makes a good paste. It should be quite smooth, and not lumpy. Alum is added in many cases when making, and, to prevent mould, some add salicylic acid.
* Carbolic, sulphate of quinine, oil of cloves, salicylic acid, oil of winter-green, and boric acid, are used to prevent fermentation and as an insecticide.
Dextrine, starch guin, or British gum is used for leather purposes. It is soluble in cold or hot water. When dry it is very brittle, and, if excessively used, is the cause of broken and blunted needles. To lessen its brittleness, glycerine is sometimes added. Dextrine is more adhesive than flour pastes, and is disliked by vermin.
Cement is made from rubber. It is very adhesive, but must be allowed to dry somewhat on the leather before being put into contact with the other substance. It dries flexible, and is proof against insect life.
Cold-water Glue is made by mixing (a) and (b), putting the mixture in a steam bath until thoroughly incorporated (a) 1 quart water, 1 lb. fish glue. The glue to soak in water all night. (6) Dissolve 21/2 oz. chloride magnesia, ,, 21/2 oz. „ calcium, in one quart of water.
Shoemakers Paste is made by taking barley-meal and, with warm water, mixing into a thick paste. Hot water is added to bring it to the required consistency. It should then be placed in a warm place to ferment, which may be ascertained by the sour smell. This is a tenacious, smooth paste, free from lumps, and is a splendid adherent.
A paste may be made from gum dragon or gum tragacanth.
There are several proprietary pastes on the market, such as the "Sphinx Shoe Paste" and "Hedoral Gum."
For affixing patent beading, an adherent made by dissolving gelatine in acetic acid may be used.