PART II. PREPARATION BY DRAFTSMEN.

GENERAL DIRECTIONS.

The work of preparing illustrations such as are used in the reports of the Geological Survey is essentially that of making finished drawings from more or less crude and imperfect material furnished by authors to illustrate certain features or phenomena discussed in their manuscripts. Each finished drawing must be so prepared that it can be reproduced in multiple by one of several processes of engraving. The author's sketches and other material are commonly called "originals"; the finished illustrations are known by the engravers as "copy." Though most engraver's copy consists of more or less elaborate drawings that are to be reproduced in facsimile by "direct" processes without the interposition of handwork, some of it consists of more roughly prepared copy which is accurate in statement but requires complete manual or "indirect" reproduction. The direct processes in use are zinc etching, half-tone engraving, photolithography, three-color half tone, photogravure, and photogelatin. The manual or indirect processes are wax engraving, wood engraving, engraving on copper and on stone, plain lithography, and chromolithography. These processes are described on pages 72-90.