As soon as the finest lines are deemed sufficiently deep, the liquor is to be poured back into the bottle. The plate must now be well rinsed with water, and dried at a heat not capable of melting the wax or var nish. The plate is now examined, and those parts which are intended to possess the lightest shade, are to be what the artist calls stopped out. This is effected by a mix ture of turpentine varnish and lamp-black, intimately ground together. Those lines which are sufficiently etched, are now to be covered with this varnish, by laying it on carefully with a camel-hair pencil. As soon as the varnish is a little hardened, the etching li quor is to be again poured on the plate, observinig the same treatment as before. When the corrosion has again proceeded till the next degree of shade is pro duced, it is again poured off, and treated as before. By this management, which depends entirely upon the skill and experience of the artist, the most delicate grada tions of shade may be produced. When the corrosion is deemed sufficient in every part, the plate must be washed clean, and then uniformly heated to remove the wax from the sides. While the plate is still warm, it must be smeared over with oil of turpentine, or olive oil, or what is cheaper, spirit of tar. Any of these readily soft en and dissolve the varnish, by which means it can easily be removed, and wiped clean with a soft cloth, or what is better, curriers shavings. If, after this, any part should still be not sufficiently corroded, every other part must be again covered with varnish ; the nicer boundaries being stopped out with the pencil and tur pentine varnish. The acid liquor is now to be applied to the bare part, the plate being surrounded with wax as before. When the additional corrosion is apparent, the wax and varnish is to be removed, and the plate cleaned as before. This may be repeated as often as may be found necessary. The plate is now in a state to takc prints from it. But it will be proper to observe, that if the etched lines are not gone over by the graver, or the dry point, the impressions will soon become imperfect from the wearing of the plate. Hence re touching is always necessary, when a great number of impressions have to be taken off. In many popular works, in which the sale is great, the plates require to be retouched several times, before all the required co pies are taken off. Hence we see how desirable it would be to use some substance harder than copper for plates. Glass has been proposed for this purpose, but several objections in etching this substance render it impractica ble. We do not know that polished hardened steel has been tried. The plates might first be hardened ; without afterwards tempering them, they might be polished with great smoothness and accuracy, by machinery similiar to that used for plate glass. That the acid would etch these plates as neatly as copper, cannot be doubted, when we recollect the beautiful ornaments put upon polished steel by etching, as we shall explain in the sequel of this article.
The etching with the hard varnish is performed in the same manner as with that already described. When the varnish is first laid on the plate, it requires to be held for some time over the fire, as the linseed oil requires some time to dry, and become stiff. When the smo king ceases, it may be removed. The sign of its being heated enough, is its acquiring such a degree of adhe siveness as to hold any thing fast that may be stuck to it. This trial is made in the margin, where no lines will be required. If the heat be continued too long, the varnish will become too hard, and will be apt to break off when scratched by the needle. In other respects,
the treatment is the same as with soft varnish.
Another variety of etching is performed with what is called the soft ground, in imitation of chalk or black lead pencil sketches. The soft ground is prepared by melting a portion of fat oil, or, what is better, veal suet, with the common etching ground, or soft varnish al ready described. The mass is to be wrapped in a piece of taffety, and laid on the warmed plate, precisely as di rected in laying on the soft varnish, observing the same treatment afterwards. When the covering is cold, take a piece of thin paper, rather larger than the plate, and damp it. Apply it to the coated surface, and turning the edge on the other side, fasten them with gum or paste. When the paper is dry, it will become stretched quite tight. All that is now necessary, is to make a black lead or chalk drawing upon the paper, in the re quired style, observing not to touch the paper in any other place than the very lines in which the pencil should move ; this may be effected by the bridge-like board, which we have already called an etching-board. When the drawing is finished, the paper must be care fully removed, taking hold of it by two corners, and gently raising these, till the opposite corners are libe rated. It will be found, that wherever the pencil has pressed upon the paper, the ground will have adhered so firmly to it, that when removed, as had been directed, the ground will be brought away by the paper, from those parts intended to be etched. The ground, how ever, in these parts is not so entirely removed as it wellId have been with the etching needle, but a number of minute particles 'email', which partially prevent the action of the acid, and thus give an effect to the print taken from such a plate the appearance of a sketch in chalk or black lead pencil. The roughness of the paper on w hich sketches are made, does not admit of the lines being completely covered with the lead or chalk ; so that if one of these lines be viewed by a magnifying glass, it will appear a mixture of black and white spots, which gives the velvety softness peculiar to this style of drawing. The accidental and irregular manner in which surfaces traced by the pencil on the soft ground are co vered with small particles of the ground, occasioned by tearing off the paper from the plate, produces an effect N ery similar in point of softness. The paper being re moved from the plate, the composition to keep the acid upon it must now be placed round the margin, exactly similar to what has been described in the common etch ing. The same rules must also be observed with respect to pouring off the acid from time to time for the pur pose of stoplung out, with the black varnish already mentioned in the common process.
It will be proper to observe, and will also appear ob vious, that the accidental way in which this chalky effect is produced, will render it impossible to make any im provement in the etching, by any manual process, either with the graver or the dry point. The impressions should therefore be taken from the plate as the acid leaves it. See AQUATINTA and ENGRAVING.
A method of imitating sketchy drawings has been in vented, which consists in making the etching upon any compact limestone, such as white marble. The stone being etched in those parts where more or less shade is required, the perfectly white parts corresponding with the polished part of the stone. The stone being wet, and daubed with a printer's ball, the rough parts re ceive the ink in proportion as they have been corroded, while the polished are left free. The paper being laid upon this, and pressure applied, will give an agreeable impression.