As I have shown, it can be applied to make or mend defective leaves of books, to fill up worm-holes in leaves, to repair drawings and pictures on wood or canvas, and when mixed with any gum which sets hard, to restore, add to, fill, or imitate woodwork. Under pressure and combined with different powders it becomes as hard as ebony and fire-proof. Its extraordinary value and general utility are as yet very far from being much known.
MENDING STONE-WORK
MOSAICS—CERESA-WORK—PORCELAIN OR CROCKERY MOSAIC
Mending or repairing stone, involving its imitations, is a widely extended branch of technical science, and one which has of late years called forth much invention. The most widely spread and ancient means of uniting and repairing this material is mortar, or the mixture of burned and then slacked lime with water. Lime is made most commonly from limestone or marble. It improves in quality when carbonate of lime in organic formation, such as sea-shells, is used; and there are degrees of excellence in these, from common oyster-shells to others of a finer kind, such as those with which the brilliantly white and hard chunam of India is made. In certain places mortar, when well made, becomes with age as hard as flint. In American towns, where anthracite coal is burned, it rots away in chimneys under the influence of sulphurous acid with great rapidity. In the Pacific Islands, where lime is made from delicate small sea-shells or coral, and mortar is like a paint or enamel, a missionary has recorded that, when he taught the natives how to make it, they whitewashed everything, even to the children, who thus became white people.
The misapplied word mastic, which suggests a gum, refers to certain modifications of mortar into which oil enters; also the oxides of lead or zinc. “Oil forms with these an insoluble soap, which includes or binds the other materials, forming, after one month’s drying, a very hard substance,” which some say is as hard as stone, but which depends entirely on the quality and combination; for I have seen so-called mastic applied to coating cheaply built houses, which cracked or crumbled away like mere plaster of Paris.
To thoroughly amalgamate mastics, it is usual to put their ingredients into casks which are two-thirds filled, and then revolved by machinery. The oil is then added. At least two days are required for the process. The following recipes for mastics are among the best, having been approved by Lehner. It may here be remarked, once for all, not only as regards mastics, but all recipes in this work, that unless the materials indicated are of the very best quality, and the processes be most thoroughly carried out, the experimenter cannot expect complete success. More than this, the experimenter must not be satisfied with a single trial. If every recipe could be at once executed by every cook, we should find the most exquisite cookery on every table in Europe. I once published the correct recipe for making objects of a peculiar kind of papier-mâché hardened. It was very easy to make. I had seen specimens of the ware, and I received the recipe from the inventor. Moreover, a great deal of money had been made by it. However, soon after I had published it I received an indignant letter from the head of a large manufacturing house, stating that they had tried my recipe and utterly failed!
French Mastic:—
| Quartz or flint sand, | parts | 300 |
| Powdered quicklime, | ” | 100 |
| Litharge, | ” | 50 |
| Linseed-oil, | ” | 35 |
Paget’s Mastic:—
| Flint sand | 315 |
| Washed chalk | 105 |
| White lead | 25 |
| Minium | 10 |
| Sugar of lead in solution | 45 |
| Linseed-oil | 35 |
The paste or “dough” thus formed should be ground with horizontal rollers in a mill, such as is used for chocolate, until all the ingredients are very thoroughly amalgamated.