Young's Demonstrative Translation of Scientific Secrets Part 9

175. DUTCH OR GERMAN GOLD

A gilding powder is sometimes made from Dutch gold, which is sold in books at a very low price. This is treated in the same way as the real gold leaf in making the true gold powder. It is necessary, when this inferior powder is used, to cover the gilding with a coat of clear varnish, otherwise it soon loses its metallic appearance. The same remark applies, though to a less degree, to Mosaic gilding.

176. COPPER POWDER

This is prepared by dissolving filings or slips of copper with nitrous acid in a receiver. When the acid is saturated, the slips are to be removed; or, if filings be employed, the solution is to be poured off from what remains undissolved; small bars are then put in, which will precipitate the copper from the saturated acid, in a powder of the peculiar appearance and colour of copper, and the liquid being poured from the powder, this is to be washed clean of the crystals by repeated levigations.

177. COMMON SIZE

The size used by painters for most sorts of common work is prepared by boiling in water pieces of parchment, and of the skins of animals and fins of fish, and evaporating the solution to a proper consistency. It only differs, however, from a solution of glue containing fewer foreign ingredients, and in not being so strong.

178. DR. JOHN'S VARNISH FOR PLASTER OF PARIS CASTS

Take of white soap and white wax, each half an ounce, of water two pints; boil them together for a short time in a clean vessel. This varnish is to be applied when cold, by means of a soft brush. It does not sink in, it readily dries, and its effect may be heightened by lightly using a silk pocket handkerchief.

179. GENERAL DIRECTIONS FOR BRONZING

This art is nothing but a species of painting, but far from being of the most delicate kind. The princ.i.p.al ingredients made use of in it are the true gold powder, the German gold, the aurum mosaic.u.m, and copper powder, (all above described.) The choice of these powders is, of course, to be determined by the degree of brilliancy you wish to obtain. The powder is mixed with strong gum water or isingla.s.s, and laid on with a brush or pencil; and when not so dry as to have still a certain clamminess, a piece of soft leather wrapped round the finger, is dipped in the powder and rubbed over the work; when the work has been all covered with the bronze, it must be left to dry, and any loose powder then cleared away by a hair pencil.

180. BRONZING IN WOOD

This may be effected by a process somewhat differing from the above, Prussian blue, patent yellow, raw amber, lamp-black, and pipe clay are ground separately with water on a stone, and as much of them as will make a good colour put into a small vessel three-fourths full of size. This mixture is found to succeed best on using about half as much more pipe clay as of any of the other ingredients. The wood being previously cleaned and smoothed, and coated with a mixture of clean size and lamp-black, receives a new coating with the above compound twice successively, having allowed the first to dry.

Afterwards the bronze powder is to be laid on with a pencil, and the whole burnished or cleaned anew, observing to repair the parts which may be injured by this operation; next, the work must be coated over with a thin lather of castile soap, which will take off the glare of the burnis.h.i.+ng, and afterwards be carefully rubbed with a woollen cloth. The superfluous powder may be rubbed off when dry.

181. IN BRONZING IRON

The subject should be heated to a greater degree than the hand can bear; and German gold, mixed with a small quant.i.ty of spirit of wine varnish, spread over it with a pencil; should the iron be already polished, you must heat it well and moisten it with a linen rag dipped in vinegar.

182. BRONZING CASTS OF PLASTER OF PARIS

There is a method of bronzing casts of plaster of Paris a.n.a.logous 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. Sh.e.l.l-LAC VARNISH

Dissolve in an iron kettle, one part of pearl-ash in about 8 parts of water; add one part of sh.e.l.l-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 was.h.i.+ng 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 Sh.e.l.l-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 pa.s.sed into the resinous solution, where the gas will be absorbed, and the lac precipitated.

185. Sh.e.l.l-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. Sh.e.l.l-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 j.a.panning.

187. j.a.pANNING

If it be woodwork you are about to j.a.pan, it must be prepared with size, and some coa.r.s.e material mixed with it to fill up and harden the grain of the wood, (such as may best suit the colour to be laid on,) which must be rubbed smooth with gla.s.s paper when dry. In cases of accident, it is seldom necessary to resize the damaged places, unless they are considerable.

188. GRINDING COLOURS IN j.a.pANNING

Be very careful in j.a.panning, to grind your colours smooth in spirits of turpentine, then add a small quant.i.ty of turpentine and spirit varnish, lay it carefully on with a camel hair brush, and varnish it with brown or white varnish, according to the colour.

189. COLOURS REQUIRED IN j.a.pANNING

Flake white, red lead, vermillion, lake, Prussian blue, patent yellow, orpiment, orchres, verditers, vand.y.k.e brown, umber, lamp-black, and siennas raw and burnt. With these you may match almost any colour in general use in j.a.panning. For a black j.a.pan, it will be found sufficient to mix a little gold-size with lamp-black; this will bear a good gloss, without requiring to be varnished afterwards.

190. TO PREPARE A FINE TORTOISE-Sh.e.l.l j.a.pAN

Take 1 gallon of good linseed oil, and 1/2 lb. of umber; boil them together till the oil becomes very brown and thick, then strain it through a coa.r.s.e cloth, and set it again to boil; in which state it must be continued till it acquires a consistence resembling that of pitch; it will then be fit for use.

191. DIRECTIONS FOR USING TORTOISE-Sh.e.l.l j.a.pAN

Having thus prepared the varnish or j.a.pan, clean well the substance which is to be j.a.panned; then lay vermillion, tempered with sh.e.l.l-lac varnish, or with drying oil, very thinly diluted with oil of turpentine, on the places intended to imitate the more transparent parts of the tortoise-sh.e.l.l; when the vermillion is dry, brush the whole over with black varnish, tempered to a due consistence with the oil of turpentine. When set and firm, put the work into a stove, where it may undergo a very strong heat, which must be continued a considerable time; if even three weeks or a month it will be the better. This tortoise-sh.e.l.l ground it not less valuable for its great hardness, and enduring to be made hotter than boiling water without damage, than for the superior beauty and brilliancy of its appearance.

192. TO MAKE CLOTH, SILK &c., WATER-PROOF

Mix equal quant.i.ties of alum and acetate of lead, and dissolve the mixture in 1-1/2 gallons of boiling water. When the solution has cooled, remove the supernatent liquid from the sediment, which consists of sulphate of lead, and is ready for use. Any article of dress, when well saturated in this liquid, and allowed to dry slowly, bears the action of boiling water, and does not permit it to pa.s.s through, although steam and air penetrate if freely.

193. CROCKERY CEMENT

Dissolve 1 oz. of common salt in 1 quart of water, bring to a boil, and put in 1-1/4 lbs. gum sh.e.l.l-lac; when it shall have dissolved, pour into cold water, and work like wax; make into small sticks.

This will make crockery as firm as a rock. Directions: Warm the stick, apply it to the broken edges, then heat the edges, place them together and hold for a minute, and they are firm.

194. A CEMENT FOR CHINA, GLa.s.s-WARE, &c.