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As will be speedily observed in the great number of recipes for mending which will be given in this book, there are many which occur frequently in different combinations; therefore it will be advisable and indispensable for those who wish to master mending as an art to indicate these as a basis.

As Sigmund Lehner has observed in his valuable work on Die Kitte- und Klebemittel, there have been such vast numbers of recipes published of late years for adhesives in various technological works, that the combination of the usual materials depends almost on the judgment of the experimenter, and every practical operator will soon learn to make inventions of his own. These materials, according to Stohmann, may be classified as follows:—

I. Those in which Oil is the basis. II. Resin or pitch. III. Caoutchouc (indiarubber) or gutta-percha. IV. Gum or starch. V. Lime and chalk.

Lehner extends the list as follows into adhesives, or cements:—

I. For glass and porcelain in every form. II. For metals not exposed to changes of temperature. III. For stoves and furnaces, or objects exposed to heat. IV. For chemical apparatus and objects exposed to corrosive liquids. V. Luting or cements, to protect glass or porcelain vessels from the action of fire. VI. Cements for microscopic preparations, for filling teeth and similar work. VII. Those for special objects, such as are made of tortoise-shell, meerschaum (ivory), &c.

Oils are divided into those (such as olive) which never become hard, and the linseed, which in time dries into a substance like gum. The latter combined with a great variety of mineral substances, such as plumbago, calcined lime, magnesia, chalk, red oxide of iron, soapstone, or with varnishes, forms insoluble “soaps,” which, as cements, resist water. They require a long time to set or become hard.