Glues are part of a larger family called adhesives. The two classes are distinguished by the fact that glue comes from organic compounds while adhesives are chemical-based. Adhering materials called epoxies, caulks, or sealants are also chemical compounds that have special additives to give them properties suitable for particular jobs or applications. Glue came into being when ancient tribes discovered that the bones, hides, skin, sinew, and other connective tissues from animals could be processed to remove collagen, the protein in these tissues. The collagen was sticky and was useful for holding things together. Milk solids, known as casein, and blood albumin can also be used as a basis for glue. Dried serum from cows' blood yields albumin that coagulates (clumps together) when it is heated and becomes insoluble in water. Fish glue was also made from the heads, bones, and skin of fish, but this glue tended to be too thin and less sticky. By experimenting, early man discovered that the air bladders of various fish produced a much more satisfactory glue that was white and tasteless. It eventually was named isinglass or ichthocol. There are three classes of substance that are called glues and that do not contain chemicals, compounds, or high-tech additives; these are bone glue, hide or skin glue, and fish glue. Technically, other sticky substances are adhesives, gums, or cements, although consumers tend to use these terms interchangeably. Plants have also been used to produce glues collectively called vegetable glues. These materials are dispersible or soluble in water and are usually made from the starches that compose many grains and vegetables. The natural gums include agar, from colloids in marine plants, algin that is derived from seaweed, and gum arabic, an extract of the acacia tree (also known as the gum tree). The substance called marine glue is used to caulk seams, but it consists of tar or pitch and is not truly a glue. The earliest evidence of use of glue can still be observed in the cave paintings made by our Neanderthal ancestors in Lascaux, France. These early artists wanted their work to last and mixed glue with the paint they used to help the colors resist the moisture of the cave walls. Egyptian artifacts unearthed in their tombs show many uses of glues; perhaps the most striking are the veneers and inlays in wood furniture, which was made using glue as early as 3,000 B.C. The Egyptians also used glue to produce papyrus. Greek and Roman artists used glues extensively; mosaic floors and tiled walls and baths are still intact after thousands of years. Furniture-making relies heavily on glues. Although there are many techniques for fastening pieces together, glue is often used either permanently or to align pieces while other connections are put in place. All of the great cabinetmakers from the sixteenth through the nineteenth centuries used glue in furniture construction, including Chippendale, Hepplewhite, Duncan Phyfe, the Adams brothers, and Sheraton. The glues used by these cabinet makers were made from animal hides, hooves, and other parts that had been reduced to jelly, then dried. The jelly was ground into power or flakes. It was remixed with water and heated gently in a glue pot. This product was brown, brittle, hard, and not waterproof. Yet this glue was the only glue available until World War I. At that time, casein glues made of milk and nitrocellulose glues were first manufactured. In the 1930s, advances in the chemical and plastics industries led to development of a wide range of materials called adhesives and plastic or synthetic resin glues. World War II led to a further flowering of this industry when neoprenes, epoxies, and acrylonitriles were invented. These were used by the military and were not available for commercial use until the late 1940s or 1950s. Since that time, highly specialized, waterproof adhesives have been developed for many industries and unique...
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