PLASTER OF PARIS. - In removing the seams left from the mould a knife or scraper is first used and the work is then rubbed with Dutch rush, or fish skin previously softened in water. The cleaning off is best done before the plaster is dry. Plaster of Paris is made very closely to resemble ivory, by the following process, invented by Mr. Franchi, an Italian figure caster: - Plaster and colouring matter, are employed in the proportions of one pound of superfine plaster of Paris, to half an ounce of Italian yellow ochre reduced to the finest powder, they are intimately mixed by passing them together through a fine sieve, after which the plaster cast is made in the usual way. It is first allowed to dry in the open air, and is then carefully heated in an oven, (one that is used for culinary purposes will answer,) the hot plaster cast when thoroughly dry, is soaked for one quarter of an hour in a bath containing equal parts of white wax, spermaceti, and stearine, heated just a little beyond the melting point. The cast on removal is set on edge that the superfluous composition may drain off, and before it cocls its surface is brushed with a brush like that known by house painters as a sash tool, to remove any wax which may have settled in the crevices, and finally when the plaster is entirely cold, its surface is polished by rubbing it with a tuft of cotton wool.

Mr. Franchi's specimens, some of which are very classical and in high relief, are cast in a peculiar manner in elastic moulds; and although he states the above to be the usual proportions of the yellow ochre for a medium tint, the quantity may be reduced or increased for paler or darker shades. He adds that the brown discoloured parts in old carvings in ivory, are sometimes imitated in water colours with a camel hair pencil before the works are dipped in the composition, which entirely defends them from the action of the air, and permits them to be washed with soap and water if so required.

Mr. Franchi was rewarded by the Society of Arts for this invention in 1846.