The Good Joshua

It is estimated that about 40 lb (18.2 kg) per year of glue are used for every person in America, and it is easy to see how and why when one looks at the extent of uses. Furniture, plumbing, shoes, books, buildings, and automobiles all use glue in some part of their construction.

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.