2fezzotinto Engraving. In this species of engraving the artist, with a knife or instrument made for the purpose, roughs over the whole surface of the copper in every direction, so as to make it suscep tible of delivering a uniform black, smooth, or flat tint. After this process the outline is traced with an etching nee dle, and the lightest parts are scraped out, then the middle tints so as to leave a greater portion of the ground, and so on according to the depth required in the several parts of the work.
Aquatinta Engraving, whose effect somewhat resembles that of an Indian ink drawin,g. The mode of effecting this is, (the design being already etched) to cover the plate with a ground made of resin and Burgundy pitch or mastic dis solved in rectified spirit of wine, which is poured over the plate lying in an in clined position. The spirit of wine, from its rapid evaporation, leaves the rest of the composition with a granulated text ure over the whole of the plate, by which means a grain is produced by the aqua fortis on the parts left open by the evapo ration of the spirit of wine. The margin of the plate is of course protected in the usual way. After the aquafortis has bitten the lighter parts they are stopt out, and the aqnafortis is again applied, and so on as often as any parts continue to require more depth. Formerly the grain used to be produced by covering the copper with a powder or some substance which took a granulated form, instead of using the 'compound above mentioned ; but this process was found to be both uncertain and imperfect. In the compound the grain is rendered finer or coarser, in pro portion to the quantity of resin intro duced. This mode of engraving was invented by a Frenchman of the name of St. Non, about 1662. He communicated it to Jean Baptiste le Prince, who died in 1781, from whom it was acquired by Paul Sandby, who introduced it through the medium of Mr. Jukes into Eng land.
Etching on Glass. The glass is covered with a thin ground of beeswax : and the design being drawn with the etching nee dle, it is subjected to the action of sul phuric acid sprinkled over willpowder ed flour of Derbyshire spar. After four or five hours this is removed, and the glass cleaned off with oil of turpentine, leaving the parts covered with the bees-. wax untouched. This operation may be inverted by drawing the design on the glass with a solution of beeswax and tur pentine, and subjecting the ground to the action of the acid.
Engraving on Stone or Lithography.— A modern invention, by means whereof impressions may be taken from drawings made on stone. The merit of this dis
covery belongs to Aloys Senefelder, a musical performer of the theatre at Mu nich about the year 1800. The following are the principles on which the art of lithography depends : First, the facility with which calcareous stones imbibe water ; second, the great disposition they have to adhere to resinous and oily sub stances ; third, the affinity between each other of oily and resinous substances, and the power they possess of repelling water or a body moistened with water. flence, when drawings are made on a polished surface of calcareous stone with a resinous or oily medium, they are so adhesive that nothing short of mechanical means can effect their separation from it, and whilst the other parts of the stone take up the water poured upon them, the resinous or oily parts repel it. Lastly, when over a stone prepared in this manner a colored oily or resinous substance is passed, it will adhere to the drawings made as above, and not to the watery parts of the stone. It was formerly thought that England did not possess a sort of stone like that of Germany, suitable to the purposes of lithography ; this, how ever, is now known to be erroneous, as the neighborhood of Bath abounds with it, being the white liar, which lies imme diately under the blue. It is also found in Scotland. The ink and chalk used in are of a saponaceous quality : the former is prepared in Germany from a compound of tallow soap, pare white wax, a small quantity of tallow, and a portion of lamp-black, all boiled together, and when cool dissolved in distilled wa ter. The chalk for the crayons used in drawing on the stone, is a composition consisting of the ingredients above men tioned, but to it is added when boiling, a small quantity of potash. After the drawing on the atone has been executed and is perfectly dry, a very weak solution of vitriolic acid is poured upon the stone, which not only takes up the alkali from the chalk or ink, as the case may be, leaving an insoluble substance behind it, but it lowers in a very small degree that part of the surface of the stone not drawn upon, and prepares it for absorbing wa ter with greater freedom. Weak gum water is then applied to the stone, to close its pores and keep it moist. The stone is now washed with water, and the daubing ink applied with balls as in printing ; after which it is passed in the usual way through the press, the process of watering and daubing being applied for every impression.