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varnish is thus prepared : Take four ounces of fat oil very clear, U*ud made of verv good linseed oil, like that used by painters:heat it in a'clean ’pot of glazed earthenware, and afterwards putto it four ounces of mastich well powdered: and stir the mixturebriskly till the whole be well melted : then pass the whole massthrough a piece of line linen into a glass bottle with a long neck,that can be stopped very securely: and keep it for use. Tomaking the soft varnish, Mr. Lawrence, an eminent English en-graver at Paris, gives the following directions : “ Take of virginwax and asphaltum, each two ounces: of black pitch and Bur-gundy pilch, each half an ounce. Melt the wax and pitch in anew earthenware glazed pot; and add to them, by degrees, theasphaltum finely powdered. Let the whole boil, till such timesas that, taking a drop upon a plate, it will break when it is cold,on beading it double two or three times, betwixt the lingers.The varnish being then enough boiled, must'be taken off the (ire ;and letting it cool a little, must be poured into warm water, thatit may work the more easily with the hands, so as to he formedinto balls; which must be rolled up, and put into a piece of taf-fely for use.” Care must be taken, 1st. that the lire be not tooviolent, for fear of burning the ingredients; a slight simmeringwill be sufficient: 2dly, that while the asphaltum is putting in,and even after it is mixed with them, the ingredients should bestirred continually with the spatula: and, 3dly, that the water,into which this composition is thrown, should be nearly of thesame degree of warmth with it, to prevent a kind of cracking thathappens when the water is too cold. The varnish ought alwaysto be harder in summer than in winter; and it will become so itboiled longer, or if a greater proportion of the asphaltum or brownresin be used.

Etching, Method of. 1. To apply the soft varnish: Theplate being well polished, burnished, and cleansed from all greasi-ness by chalk or Spanish white, fix a hand-vice on the edge of theplate where no work is intended to he, to serve as a handle formanaging it when warm : then put it upon a chafing-dish, in which jthere is a moderate lire; observing to hold it so that it may notburn: keep the plate over the fire till it be so hot that the varnishbeing brought into contact with it max melt: then cover the wholeplate equally with a thin coat of the varnish ; and while the plate ■w vvarm, and the varnish upon it in a fluid stale, beat every partot tlie varnish gently with a small ball or dauber made of cottontied up in tatfely ; which smooths and distributes the varnishequally over the plate. When the plate is thus uniformly and ithinly covered with the varnish, it must be blackened by a piece !ot flambeau, or of a large candle which afiords a copious smoke;sometimes two, or even four candles are used together for thesake of dispatch, that the varnish may not grow cold: which if itdoes during the operation, the plate must be heated again, that itmay be in a melted state when that operation is performed : butgreat care must be taken not to burn it; which, when it happens,may be easily perceived by the varnish appearing burnt and losingits gloss. I he following expedient is used, for the commodiousiyblackening the varnish, particularly where the plates are large': ia strong hook is fixed in the root of the room, through whichpasses four pieces of cord of equal length, at the end of which arefixed lour iron rings of about four inches diameter, for supportingthe coiners of the plate. The plate being thus suspended in theair, with the varnished side downwards, may be blackened withgreat convenience: but this is not, however, absolutely requisite,except in the case of large plates that could not, without difficulty,be held up, unless this or some other such contrivance were madeUse of. T| ie flambeau or c:ndle must be kept at a due distance>rom the plate, lest the wick touch the varnish, which would sullyand mark it. If the smoke has not penetrated the varnish, theplale must lie again placed for some little lime over the chafing-dish ; and as the plate grows hot, the varnish will melt and incor-porate v. ith the black which lav above it, so that the whole willbe equally pervaded by it. 'The greatest caution should be usedto keep all the time a moderate fire ; and to move frequently theplate, and change the place of all the parts of it, that the varnish.may be alike melted every where, and kept from burning. Caremust also be taken, that during this time, and even till the varnish beentirely cold, no tilth, sparks, or dust, fly on it ; for they wouldthen stick last, and spoil the work. 2. 'the method of applyingthe haul varnish is precisely the same as for the soft; being spread

equally over the warm plate with the tallfety ball, and smoked inthe same manner: only after it is smoked, it must be baked, ordried, over a gentle lire of charcoal, till the smoke from the var-nish begins to decrease ; taking care not to overheat the plale,which would both soften and burn the varnish. The plate beingprepared, and an exact drawing of tbe outlines of the design madeupon thin paper, the other side of the paper must be well rubbedwith chalk or Spanish whitening, or, rather with red chalk scrapedto a powder. The loose chalk is cleaned oIT with a linen rag:then the stained side of the paper is laid upon the varnish, fixingthe comers to the plate with wax or wafers, to prevent its shuf-fling; and with a blunted needle or pointer the drawing is slightlytraced, and communicates to the varnish an exact outline ot the.design to be etched.- A variety of pointers is necessary for thework. Those used for the broad large strokes ought to be veryblunt, exceedingly round, and well polished at the point; the soleof a shoe answers very well for polishing the points. The finest'ought to he as sharp as a needle. If any scratches or false strokes •happen in the working, they must be stopped up with a hair pen-cil dipped in Venetian varnish, mixed with lamp black, by whichthese places will be defended from the action of the aqua fortis.The next operation is that of eating or corroding the plate withaqua fortis. A border of soft wax (being a composition of bees’-wax melted with a littice Venice turpentine and tallow) must befastened round the plate about an inch high, in the form of a littlewall, to contain the aqua fortis. At a corner of this border agutter is made (o pour tiie aqua fortis off the plate. Take a duequantity of the refiner’s aqua fortis ; mix it with half its quantityof common water ; and pour it gently on, till it rise about a fin-ger’s breadth above the surface of the plate ; when the aquafortis will soon exert its action in the hatches which have beenstronglv touched ; but those more weakly engraved will appear atfirst clear, and of the colour of the copper. The menstruummust therefore be suffered to continue on the plate till its effectsbecome visible on the more tender parts: then the aqua lordsshould be poured off, the plate washed with clean water, and driedbefore the fire: (hen take a small pencil dipped in the Venetianvarnish, and cover with it the lighter parts of the plate. Theaqua fortis must then be again poured on, and continued a longeror shorter time, according to tiie strength of the menstruum, orthe nature of the engraving ; when it must be again poured off,and the plate immediately washed with water. When the aquafortis is on the plate, a feather should be used to cleanse away thefoulness of the verdigris that gathers in the hatches, when the aquafortis operates on them, and to give it more room to exert its ac-tion - , for by moving the aqua fortis to and fro, on the plate bythe feather, and brushing away the black saline matter where itappears to be formed, the hatches will be cleansed, and the aquafortis exert its whole force equally on every part. The plate be-ing thus sufficiently corroded by the aqua fortis, and well washedwith water, it must be wanned at the lire, and the border of waxremoved ; after which, it must be made hotter till the varnishmelt; then it must he well wiped with a linen cloth, and after-wards rubbed heartily with oil of olives; when it will be ready' tobe retouched and finished hv the graver. See Engraving.

Etching on Gi.ass. Glass resists the action of all the acids,except the fluoric acid. By this, however, it is corroded in thesame manner as copper is by aqua fortis; and plates of glass maybe engraven in the same manner as copper. There are severalmethods of performing this. We shall first describe the mode ofetching by means of the fluoric acid in the state of gas. Havingcovered over the glass to be etched with a thin coat of virgin-wax(which is only common bees’-wax bleached white,) draw the de-sign upon it in the same manner as in etching on copper. Thentake some fluor spar, commonly called Derbyshire spar, pound itfine, and put it into a leaden vessel, pouring some sulphuric acidover it. Place the glass with tiie etched side lowermost over thisvessel, tw’O or three inches above it. Apply a gentle heat to theleaden vessel ; this will cause the acid to act upon the fluor spar,and disengage the gas, which will corrode the glass. When it issufficiently corroded, remove the wax by oil of turpentine. Thisetching may be also performed by raising a margin of bordering-wax all round the glass, in the same manner as on copper, andpouring on the liquid fluoric acid, which acts upon the glass.The method of making this acid is described under fluoric acid.

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