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means of the fluoric acid in the state of gas. Having covered over the glass to be etched with a thin coat of virgin-wax (which is only common bees-wax bleached white,) draw the design upon it; in the same manner as in etching on copper. Then take some fluor spar, commonly called Derbyshire spar, pound it fine, and put it into a leaden vessel, pouring some sulphuric acid over it. Place the glass with the etched side lowermost over this vessel, two or three inches above it. Apply a gentle heat to the leaden vessel; this will cause the acid to act upon the fluor spar, and disengage the gas; which will corrode the glass. When it is sufficieutly corroded, remove the wax by oil of turpentine.

This etching may be also performed by raising a margin of bordering.wax all round the glass, in the same manner as on copper, and pouring on the liquid fluoric acid, which acts upon the glass. The method of making this acid was described under the article fluoric acid, in ches mistry.

A third method of etching on glass is as follows: Having put the wax on the glass, draw your design, and raise a margin all round it. Then put pounded fluor spar, with some sulphuric acid diluted with water, upon the glass. The sulphuric acid will disengage the fluoric, which will be absorbed by the water, and corrode the glass.

In all the above-mentioned methods, some of the gas is let loose in the apartment, and is exceed. ingly suffocating. To remedy this inconvenience, an apparatus was contrived by the editor of this work, some years ago, and is found to answer perfectly.

A, Fig.5., Plate XVII., Vol. 1., is a cylindrical leaden vessel, having a rim B all round it, made like Count Rumford's steam rim for cooking vessels, into which is put a little water. Into this rim fits a cover c, having a pipe d coming from it, which is inserted into a large oblong vessel e of sheet lead, or iron well tinned, having a rim and cover similar to the vessel A, only the cover has no aperture. The fluate of lime powdered and the sulphuric acid are put into the leaden vessel A, which is placed upon a stand made of wire, having a lamp to heat the contents of the vessel over it. As soon as the gas is evolved it ascends, and not being able to escape through the rim B, on account of the water, which condenses a portion, it proceeds through the tube into the large vessel e, in which is placed, upon stands of wire, the glass prepared for etching by drawing through a varnish, as above described.

In this vessel the gas collects, and acts upon the glass : the rim with water prevents any noxious fumes from escaping into the room. The vessel e is placed upon a stand of such a height as to agree with that of the lamp. In this manner the process may be conducted with the utmost ease and elegance.

Beautiful ornaments may thus be etched on glass, and applied to decorate windows, by painting the figure of the ornament on panes of glass with enrgravers' stopping varnish, and then exposing the panes to the action of the gass in the vessel e. The gas will corrode all the surface of the glass, except where the varnish has been put, and give it much the appearance of ground glass, which may be rendered more or less opaque by lengthening or shortening the process. The parts

where the varnish was applied will continue transparent and seem extremely bright. It is to be noticed, when the liquid fluoric acid is used, the lines which have been etched continue still transparent; but when the gas has been employed, the line is white and opaque, as if cut by a wheel.

LITHOGRAPHY.

This art is so called, because the impressions are produced from drawings made on stone. It was invented by Aloys Sennefelder, a German, about the year 1800.

There are several styles of drawing employed in lithographic prints. The chief are, the line manner, and the chalk manner. In the line manner, which is similar in its effect to the line engraving on copper of second rate quality, lines are drawn on a stone with a particular sort of ink, by means of pens of various kinds, or a camels-hair pencil.

In both these methods, the same kind of stone is used; but in the line manner, the stone must be polished smooth with pumice-stone, whereas, for the chalk it is made a little rough, by grinding with sand. The stone must be calcareous and of a light colour. The white lias in this country answers tolerably well, but is not so fit as the German stones.

The lithographic ink is composed of equal parts of tallow, bees-wax, shell lac, and common soap, with a sufficient quantity of lamp-black to colour it. These ingredients are mixed by heating them,

and even burning them in an iron vessel. When cold, the mass is rubbed on a tile with water, like Indian ink, and put into a pen or brush.

The lithographic chalk is formed of 2 oz. of tallow, 24 oz. of bees-wax, 1 oz. of shell lac, and 1į oz. of common soap. These are also united by heating as before; when cold it is cut into slips, and used as a crayon.

When the drawing is made on the stone with the pen and ink, or with the chalk or crayon, some water, having in it a little nitric acid, is poured over the stone, which slightly corrodes the surface; gum-water is then laid on with a brush, and the stone is left to dry; it is now ready for printing from.

To print from the stone, the printer proceeds to wet the surface of it with a sponge with water, and then applies the printing ink, by a roller.

The printing ink, made of equal parts of burnt oil or varnish, and lamp-black, sometimes with the addition of wax and tallow, adheres to the lines which have been drawn with the lithographic ink on the stone, while the water prevents it from sticking to the rest of the surface. The lines alone are thus charged with printing ink. Some damped paper is now laid upon the stone, and passed through a press, by which an impression is obtained. The stone is again wetted, and the printing ink applied for a second impression, and so on.

The process is the same for printing chalk drawings; but they are more difficult to print, and give fewer impressions.

This art has made considerable progress on the continent; in this country it has advanced more slowly, chiefly from the secresy employed in the

processes of printing. On this account, its advantages were not well comprehended, it being difficult to institute a just comparison between this and the other species of engraving, which are in this country carried to such a high degree of perfection. It is now, however, rapidly improving, since artists have been induced to take it up, and we shall probably soon equal, if not surpass, our continental neighbours.

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