520 CALLOTECHNICS. 



off the acid, and covering that part with varnish ; and the rest may 

 then be bitten deeper, at pleasure. 



Mezzotinto engraving, is executed by first roughening the copper 

 surface all over mechanically, and then burnishing, or smoothing down 

 again, those parts which are to be light in the picture. Aquatinta 

 engraving, is usually performed by sprinkling the plate over with 

 finely powdered mastic, and then heating it till the particles soften 

 and adhere to the plate. Those parts which are to be entirely white, 

 are then completely covered over with varnish, as in etching ; and 

 the specks of varnish on the remaining part, protecting numerous 

 small points from the acid, cause the dark parts of the prints to be 

 covered with fine white dots, which produce a pleasing effect. The 

 use of steel plates, instead of copper, for engraving, was, we believe, 

 introduced by our countryman, Mr. Perkins. The plates are ren- 

 dered soft for the engraver ; but afterwards hardened by tempering, 

 and thus rendered very durable. Lithography, or stone printing, is 

 executed from a simple 'drawing, made on porous, calcareous stone, 

 with an oily ink or crayon, which drawing is firmly fixed, or ren- 

 dered permanent, by the action of a dilute acid. On moistening the 

 stone, the oily lines or dots remain dry ; and then, on applying the 

 ink, it is repelled by the wet parts, and adheres only to the drawing; 

 which is thus transferred to the paper, by means of a roller press. 



3. The art of Paper making, resembles that of cloth making, 

 in producing extended surfaces from vegetable fibres ; but differs so 

 much in the mode of producing them, and in the use to which they 

 are applied, that it may properly be mentioned here. The best paper 

 is made of white linen rags ; which are first washed and ground in 

 the paper mill ; in which they pass between sharp revolving knives 

 or cutters, till they are reduced to a fine pulpy substance, uniformly 

 diffused in the water. For paper made by hand, a quantity of this 

 pulp is taken up on a sieve ; and, the water running through, it is left 

 as a continuous sheet, which is then removed and pressed. For ma- 

 chine paper, the pulp is received on a revolving, cylindrical sieve ; 

 which discharges the water, but retains the pulp, and delivers it on 

 another cylinder, in a long sheet : and it is then pressed, by passing it 

 between rollers. Writing paper, before being pressed, is sized, with 

 a solution of glue or gelatin, which renders it smoother, and prevents 

 common ink from spreading upon it. Printing paper, is usually 

 unsized, and therefore bibulous, or capable of absorbing water freely. 



The process of Book binding, commences with the folding of the 

 sheets into leaves, and the arrangement of them, according to the 

 signatures ; which are letters, or numbers, placed at the bottom of 

 the pages, at certain intervals; by reference to which, the labor of 

 counting the pages is avoided. The leaves are then stitched together 

 at the back edges ; during which operation they are kept in place by 

 a frame, holding the threads to which they are fastened: and the 

 whole back is firmly compacted, by covering it with glue. The cover 

 is then applied, and secured to the body of the book, by the ends of 

 the threads, left protruding for that purpose. The blank leaves at 

 the beginning and end of a book are technically called fly leaves ; 

 and ought to b of sized paper, that they may be written upon with 



