FROM THE DRAWING (4½ × 2½) ON ALLONGÉ PAPER
(RIGHT SIDE).
It is also worth knowing that a good grained drawing may be made with litho-chalk, by taking a piece of dull-surfaced paper, like the kind generally used for type-writing purposes, pinning it tightly upon glass- or sand-paper and then working upon it, keeping it always in contact with the rough sand-paper underneath. A canvas-grain may be obtained by using the cover of a canvas-bound book in the same way.
Both the albumen and the bitumen processes are practised with the aid of acids upon zinc. In the first named the zinc plate is coated with a ground composed of a solution of white of egg and bichromate of ammonia, soluble in cold water. A reversed photographic negative is taken of the drawing and placed in contact with the prepared zinc plate in a specially constructed printing-frame. When the drawing is sufficiently printed upon this albumen surface, the plate is rolled over with a roller charged with printing-ink thinned down with turpentine, and then, when this inking has been completed, the plate is carefully rubbed in cold water until the inked albumen has been rubbed off it, excepting those parts where the drawing appears. The lines composing the drawing remain fixed upon the plate, the peculiar property of the sensitized albumen rendering the lines that have been exposed to the action of light insoluble. The zinc plate is then dried and sponged with gum; dried again, and then the coating of gum washed off, and then inked again. The plate, now thoroughly prepared, is placed in the first etching bath, a rocking vessel filled with much-diluted nitric acid. There are generally three etchings performed upon a zinc block, each successive bath being of progressively stronger acid; and between these baths the plate is gummed, and powdered with resin, and warmed over a gas flame until the printing-ink and the half-melted resin run down the sides of the lines already partly etched; the object of these careful stages being to prevent what is technically termed “under-etching”—that is to say, the production of a relief line, whose section would be thus:
instead of
. The result in the printing of an under-etched block would be that the lines would either break or wear down to nothingness, whereas a block showing the second section would grow stronger and the old lines thicker with prolonged use. The section of a wood engraving is according to this second diagram.