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aperture must not be opened till the fluids have compleely separated themselves from each other. It is then to be opened ; by which means the liquid which has taken the lowest place by its greater gravity, viz. the nitro-muriatic acid will run off; after which, the aperture is to be shut, and tha funnel will then be found to contain nothing but ether mixed wlth the gold, which is to be put into well-closed bottles, and preserved
In order to gild iron or steel, the metal must first be well polished with the finest emery, or rather with the finest crocus martis, or colcothar of vitriol, and common brandy. The auriferous ether is then to be applied with a small brush; the ether soon evaporates, and the gold remains on the surface of the metal. The metal may then be put into the fire, and afterwards polished. By means of this auriferous ether, all kinds of figures may be delineated on iron, by employing a pen, or fine brush. It is in this manner, probably, that the Sohlinger sabre blades are gilded.
Instead of ether, the essential oils may be used; such as oil of turpentine, or oil of lavender, which will also take gold from its solution.
Cold Gilding of Silver.-L'issolve gold in the nitro-muriatic acid, and dip some linen rags in the solution; then burn them, and carefully preserve the ashes, which will be very black, and heavier than common. When any thing is to be gilded, it must be previously well burnished; a piece of cork is then to be dipped, first into a solution of salt in water, and afterwards into the black powder ; and the piece, after being rubbed with it, must be burnished. This powder is frequently used for gilding delicate articles of silver.
Gilding of Brass or Copper.--Fine instruments of brass, in order that their surface may be kept longer clean, may be gilded in the following manner.
Provide a saturated solution of gold, and having evaporated it to the consistence of oil, suffer it to shoot into crystals. These crystals must then be dissolved in pure water, and the articles to be gilded being immersed in it, are then to be washed in pure water, and afterwards burnished. This process may be repeated several times, till the articles have been well gilt. A solution of gold crystals is preferred to a mere solution of gold; because, in the latter, there is always a portion of free acid, which will not fail to exercise more or less action on the surface of the brass or copper, and injure its polish.
Grecian Gilding:- Dissolve some mercury in muriatic acid (spirits of salts), which will give a muriate of mercury. Mix equal parts of this and sal ammoniac, and dissolve them in aqua fortis. Put some gold into this, and it will dissolve. When this is applied to silver, it becomes black; but by heating, it assumes the appearance of gilding.
To make Shell-Gold.
Grind up gold-leaf with honey, in a mortar; then wash away the honey with water, and mix the gold-powder with gum-water. This may be applied to any article with a camel's-hair pencil
, in the same way as any other colour.
Wood, paper, &c. are silvered in the same manner as gilding is performed, using only silver instead of gold-leaf.
To Silver Copper or Brass. Cleanse the metal with aqua fortis, by washing it lightly, and then throwing it into the water ; or by scouring it with salt and tartar with a wire-brush, Dissolve some silver in aqua fortis, and put pieces of
copper into the solution; this will throw down the silver in a state of metallic powder, Take fifteen of twenty grains of this silver powder, and mix with it two drachms of tartar, the same quantity of common salt, and half a drachm of alum; rub the articles with this composition till they are perfectly white, then brush it off, and polish them with leather.
Another method. Precipitate șilver from its so: lution in aqua fortis by copper, as before ; to half an ounce of this silver add common salt and sal ammoniac, of each two ounces, and one drachm of corrosive sublimate; rub them together, and make them into a paste with water. With this, copper utensils of every kind, that have been previously boiled with tartar and alum, are rubbed l; after which they are made red hot and polished.
To Silver the Dial-plates of Clocks, Scales of Ba
rometers, fc. Take half an ounce of silver lace, add thereto an ounce of double refined aqua fortis; put them into an earthen pot, and place them over a gentle
fire till all is dissolved, which will happen in about five minutes; then take them off, and mix it in a pint of clear water; after which, pour it into another clean vessel, to free it from grit or sediment; then add a spoonful of common salt, and the acid, which has now a green tinge, will immediately let go the silver particles, which form themselves into a white curd; pour off the acid, and mix the curd with two ounces of salt of tartar, half an ounce of whiting, and a large spoonful of salt, more or less, according as you find it for strength. Mix it well up together, and it is ready for use.
Having well cleared the brass from scratches, rub it over with a piece of old hat and rotten-stone, to clear it from all greasiness, and then rub it with salt and water with your hand: take a little of the before-mentioned composition on your finger, and rub it over where the salt has touched, and it will adhere to the brass and completely silver it. After which, wash it well with water, to take off what aqua
fortis may remain in the composition; when dry, rub it with clean rag, and give it one or two coats of varnish, prepared according to the directions given under the article varnishes.
This silvering is not durable, but may be improved by heating the article, and repeating the operation till the covering seems sufficiently thick.
The coat of silver applied to the surface of the copper by the means mentioned above, is very thin, and is not durable. A more substantial method of doing it, is as follows: form small pieces of silver and copper, and tie them together with
wire, putting a little borax between. The proportion of silver may be to that of the copper as one to twelve. Put them into a white heat, when the silver will be firmly fixed to the copper. The whole is now made to pass between rollers, till it is of the required thickness for manufacturing various articles.
To make French Plate.
Heat the copper articles intended to be plated, and burnish silver-leaf on it, with a burnisher.
To make Shell Silver.
leaf-silver with gum-water or honey ; when
have ground it, wash away the gum or honey, and use the powder that remains with gumwater, or glaire of eggs. This is laid on with a hair-pencil.
To silver Looking Glasses. The following apparatus must first be prepared.
1. A square marble slab, or smooth stone, well polished, and ground flat; the larger the better; with a frame round it, or a groove cut in its edges, to keep the superfluous mercury from running off.
2. Lead weights, covered with cloth, to keep them from scratching the glass; from one pound weight to twelve pounds each, according to the size of the glass which is laid down.
3. Rolls of tinfoil.
Cut the tinfoil a little larger than the glass every way, and lay it flat upon the stone; and with a straight piece of hard wood, about three inches