When gilding is pale and dirty, it may be revived by means of what is called gilding wax, a composition of yellow wax, bole ([127]), verdigris ([230]), and alum.
A very beautiful gilding upon metals, and particularly upon silver, is effected by soaking clean linen rags in a solution of gold made by aqua regia ([207]). The rags are dried and burnt; and the ashes are carefully preserved. These ashes are used by taking a sound cork, moistening it with a little water, dipping it into the ashes, and then rubbing strongly a portion of them on the surface of the silver, which should be perfectly clean and bright. By this simple and economical process, it will be covered with an extremely thin coating of gold, the colour and brilliancy of which may be heightened by burnishing. The ornaments upon snuff-boxes, fans, and various kinds of trinkets, are merely thin plates of silver, gilded in this manner.
The edges of tea-cups, and other similar articles, may be gilded, though not in a very durable manner, by applying a thin coat of amber varnish ([224]), and then placing leaf-gold upon it. When the varnish is dry, the gold is to be burnished.
Gold, in a state of solution, is sometimes used for staining marble, ivory, ornamental feathers, and other articles, a purple-red colour, which cannot be effaced. By chemical processes an oxide ([21]) is obtained from this metal, which is employed for giving those beautiful shades of lilac, rose colour, red and purple, which we observe in glass and porcelain.
A gold powder for painting may be made by uniting one part of gold with eight parts of mercury ([228]), and afterwards evaporating the latter by heat.
The article denominated gold wire is generally silver wire gilded, very little wire being made entirely of gold. Its uses are chiefly for embroidery and filagree work. Gold thread consists of flatted silver gilt wire, laid over a thread of yellow silk, by twisting it in a machine with iron bobbins. It is of this, and not of gold, that the article called gold lace is made. The Chinese, instead of flatted wire, use slips of gilt paper, which they interweave in their stuffs, and twist upon silk threads.
228. MERCURY, in its native state, is called quicksilver, and is found in small globules of shining, silvery appearance, scattered through different kinds of stones, clay, and ores. It is nearly fourteen times heavier than water.
The principal ore of mercury, and that from which the metal is chiefly obtained, is cinnabar. This is of red colour, and consists of mercury mineralized with sulphur. It is sometimes found in a massive state, sometimes in grains, and sometimes crystallized; and chiefly among rocks of the coal formation.
The most productive mines of cinnabar are in the palatinate of Germany, at Idria in Carniola, and at Almaden in Spain. Those of Idria are supposed to be more valuable than any of the others. Their first discovery, which was somewhat more than three hundred years ago, was made in a very extraordinary manner. This part of the country was then much inhabited by coopers; and one of the men, on retiring from work in the evening, placed a new tub under a dropping spring, to try if it would hold water; and, when he came in the morning, he found it so heavy that he could scarcely move it. Examining into the cause of this extraordinary circumstance, the man observed that it was owing to a shining and ponderous fluid which was at the bottom. The affair was noised abroad, and a society of persons was formed to search further, and discover the mine from which this quicksilver had flowed. Such was their success that the reigning Duke of Austria paid them a compensation for the discovery, and took the mine into his own possession. The greatest perpendicular depth of this mine is now more than 830 feet. It is descended by buckets, or by ladders placed obliquely in a zigzag direction. In some parts of the mine the pure metal flows in small streams, so that in six hours a man has been known to collect more than thirty-six pounds weight of it. In other parts it is found in a multitude of little drops, either in ores or in clay. The whole produce of the mine is said to exceed a hundred tons weight of mercury per annum.
It has been asserted that, several years ago, in digging out clay for the foundation of a house opposite to the King’s Arms inn, in the street called Hyde-hill, in Berwick-upon-Tweed, a quantity of native mercury was discovered. The clay, when dug out, lay for some time in the place to which it was conveyed; and the mercury was observed to exude from the small fissures or cracks that were formed as it dried. It is said that, several years afterwards, in making some alteration in the yard of the same house, the workmen penetrated into the same bed of clay; and that it then appeared to be impregnated with native mercury, which ran out in small globules.