Babbitt—Emerald Green; sometimes light mixture of India Ink.
Copper—Purple Lake.
It is sometimes found necessary to prepare a highly finished and shaded drawing of the work in hand. Such elaborations, in fact, are much admired by the uninitiated, although the complete shading of the drawing is no criterion as to the scientific value of the machine. An illustration of this is told in the note.
Note.—A consulting engineer had to lay before a board of directors plans of horizontal engines for their consideration. One of these drawings was of a very superior machine, but being only depicted lineally was at once rejected by them, for a highly finished representation of a very inferior apparatus. The engineer, wishing to induce the board to decide for the best, suggested that the matter should be postponed to a future day, and in the meantime had the drawing of the superior machine highly colored and finished. At the next meeting the directors unanimously decided that this was the very one which they preferred and had chosen.
Reproducing Drawings.
When once finished, one or more copies of drawings are frequently required; these are produced, 1, by blue printing, as described before; 2, by tracing. A tracing is a mechanical copy of a design or drawing, made by reproducing its lines as seen through a transparent medium—as tracing-cloth or tracing-paper.
Tracing-cloth is a thin linen fabric, coated with size; this is called tracing-lines; tracing-paper is so prepared as to be transparent, so that it will receive marks either in pencil or with pen and ink.
Tracing-cloth must be fastened to the board, over the drawing, by pins or other tacks; moisture or dampness should be carefully avoided and the drawing done on the smooth side of the cloth.
When tracing cloth will not take ink readily a small quantity of pounce may be applied to the surface of the cloth and distributed evenly with a piece of cotton waste, chamois, or similar material, but the pounce should be thoroughly removed—by washing—before applying the ink.
In making tracings the same order is followed as described under the section “Inking”—to repeat: 1, ink in the small circles and curves; 2, ink in the larger circles and curves; 3, then all the horizontal lines, beginning at the top of the drawing and working downward; 4, next ink in all the vertical lines, commencing at the left and moving back to the right; 5, draw in the oblique lines; 6, all the center lines red (carmine), and dimension and reference lines in blue (Prussian blue) or vice versa. The figuring and lettering should always be done with India ink, thoroughly black.