182. BRONZING CASTS OF PLASTER OF PARIS
There is a method of bronzing casts of plaster of Paris analogous to that which we have above given for bronzing wood, but it is not in much repute. Such figures may be beautifully varnished by means of Dr. John's varnish, receipt No. 178. Casts of plaster of Paris may be made by receipt No. 167.
183. SHELL-LAC VARNISH
Dissolve in an iron kettle, one part of pearl-ash in about 8 parts of water; add one part of shell-lac, and heat the whole to ebullition. When the lac is dissolved, cool the solution, and impregnate it with chlorine, till the lac is all precipitated. The precipitate is white, but its colour deepens by washing and consolidation; dissolved in alcohol, lac bleached by the above process yields a varnish which is as free from colour as any copal varnish.
184. CHLORINE FOR SHELL-LAC VARNISH
This may be formed by mixing intimately eight parts of common salt, and three parts of the black oxide of manganese in powder; put this mixture into a retort, then pour four parts of sulphuric acid, diluted with an equal weight of water, and afterwards allowed to cool upon the salt and manganese; the gas will then be immediately liberated, and the operation may be quickened by a moderate heat. A tube leading from the mouth of the retort must be passed into the resinous solution, where the gas will be absorbed, and the lac precipitated.
185. SHELL-LAC VARNISHES OF VARIOUS COLOURS
These may be made by using ant colour in fine powder with the varnish, in the following manner: rub up the colour with a little alcohol or spirits of turpentine till it becomes perfectly smooth, then put it into the cup with the varnish. Shell-lac varnish is the best spirit varnish we have, and may be made any colour by the above process.
186. GOLD OIL-COLOUR, OR SIZE
The English method of preparing the colour in size, which serves as the ground on which the gold is laid, is, to grind together some red oxide of lead with the thickest drying oil that can be procured, the older the better. To make it work freely, it is mixed, before being used, with a little oil of turpentine, till it is brought to a proper consistence. The above four receipts are used in japanning.