Publisher's Synopsis
This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1894 edition. Excerpt: ... In his 'Maniere de copier sur le Verre colore les Pierres Gravies' in the 'Memoires de l'Academie Royale des Sciences' (Ann DEGREESe, MDCCXII. Paris, MDCCXIV.), pp. 189-97, M- Guillaume Homberg speaks of the need for each person who attempts the matter to invent the process afresh, as it is always kept a secret by those who follow the use of it for a livelihood. He had himself to go through something of the kind, and, having been aided by the influence of the Duke of Orleans and of Madame, he was allowed to reproduce all the gems of the Royal Cabinet and those (pretty numerous) of Madame. He attained such perfection that many could not distinguish his copies from the originals. He describes his process as simply taking a mould in fine earth, en une terre fort fine, on which is pressed a piece of glass softened by fire or half melted. To prevent the ill effect of partial fusion of the mould by the glass, the best earth for the mould is the kind of chalk called tripoli. Of the two sorts of this, French and Levantine, the latter, commonly called Venice tripoli, is the best. It should be soft, like velvet to the touch, and free from admixture of other earths or of grains of sand. Both kinds, however, have their uses, as 74 follows: --Pound French tripoli in an iron mortar and pass it through a hair sieve, and keep for use. The Venice tripoli should be scraped with a knife or a piece of glass, very fine and very little at a time, it should then be passed through a very fine silk sieve and pounded in a glass mortar with a glass pestle. The finer it is the better the impression. Tripoli cannot be treated with water (like emery) to select the finest powder, because this causes the particles to separate on drying, which produces a granular appearan
