This section is from the "A Complete Dictionary of Dry Goods" book, by George S. Cole. Also available from Amazon: A complete dictionary of dry goods and history of silk, cotton, linen, wool and other fibrous substances,: Including a full explanation of the modern processes ... together with various useful tables.
Rubbers. A general term used to designate both lined and unlined rubber footwear. Many people suppose that rubbers are made by melting the material and running it into molds. Such is not the case. The manufacture of rubber shoes is not very much different from the manufacture of leather shoes. They are made on lasts in the same manner, but instead of being sewed they are cemented. About seventy per cent of pure rubber is all that is contained in the manufactured article. The best Para gum costs ninety-five cents a pound on the wharf at New York. In the smallest pair of rubber shoes there are about two ounces of pure rubber, and from that, on up to probably four pounds in a pair of heavy rubber boots. Old rubbers are ground up, lining and all, into what is called "rag carpet," which is used for insoles. The work is nearly all done by hand, the factories employing men, women and children. A boot-maker gets twenty cents a pair for making boots, and a good workman can turn out from ten to twelve pairs a day. The raw material comes mainly from South America, and is of a spongy nature and an earthy color. First, the rubber is put into warm water in order to soften it and remove the dirt and other impurities. It is then put into a masticating machine which tears it into very small pieces. Still warm and somewhat adhesive in consequence, these small fragments are quickly spread out into a thick sheet, which travels between the rollers one inch apart; the rollers press the fragments together and they adhere slightly in the form of a thick blanket - two feet wide and six feet long. These sheets are next dried and passed between large hollow steel rollers heated with steam internally, which compress the material into soft, thin sheets. Then it is taken into the compounding room where it is mixed with a compound and vulcanized. The chemical materials (sulphur, etc.) being added, the sheets are folded up and kneaded well together. This kneading process is performed by passing it several times through the hot rollers, folding it after each, and rolling it into a dough-like mass. When this operation is completed, it is finally rolled out into thin sheets several yards in length, which are reeled off on cold rollers, so as to allow cooling. It is then ready to be cut into "uppers" for the cheapest kind of rubbers, which are unlined. The better grades are lined with cotton cloth of different colors, and sometimes with other materials, as felt. The lining is made fast to the rubber sheet by passing the piece of cloth through the rollers simultaneously with the rubber in the last process, a firm adhesion of the two being effected by the heat and moisture. Another machine is so constructed that it produces a sheet thick enough for the soles, and on one surface a roughening is made by engraved lines crossing each other to prevent the soles from slipping in wet weather or on icy ground. Another ingenious pressure forms the heels. After the sheets for the uppers and heels have been cooled and reeled off, they pass through the cutting machines and are here cut in different sizes and shapes. Some cut out the inside lin. ing and the outside uppers for fronts and heel stepping, while others with great nicety cut the heeled-soles out. These various parts are now taken to the " makers," usually females, and the cast-i ron " last" is rapidly covered over with the different pieces, beginning with the insole and lining, the edges of which are cemented with a composition containing guttapercha, which produces a firm adhesion. The sole is then fitted on with equal facility, and the workman then runs a wheel-tool round the edge and other parts to produce the representation of " seam " marks. They are next coated with a varnish which quickly hardens, and are transferred to vulcanizing ovens where they are submitted to a high degree of heat, which produces a chemical union between the rubber and other materials mixed with it at the beginning of the operations. When taken from the ovens they are removed to the packing-room, where they are boxed and shipped. There are twenty rubber boot and shoe factories in the United States, each with a capacity of 25,000 pairs per day, whose products are shipped to every civilized country on the globe. These factories make special shapes for different countries, those for China and Japan not being at all suitable for Turkey or Mexico. [See India-rubber]