If tracings are required to be tinted or shaded, the color may be applied before the tracing is cut off, or what is more usual, the color may be applied on the back of the tracing; then there is no liability to wash out the lines.
Mechanical drawings are seldom tinted, but are mainly produced in India ink. Where, however, a fine effect is desired, working drawings are colored, so as to show at a glance the material of which the different parts are to be made.
The colors required are few but should be of the best quality. Besides India ink the following water-colors are generally used:
1, Neutral-tint. 2, Prussian Blue. 3, Chrome Yellow. 4, Gamboge. 5, Raw Sienna. 6, Carmine. 7, Vermillion. 8, Venetian Red. 9, Sepia. 10, Indigo. These come in hard cakes.
Certain colors and tints represent different metals and materials as follows:
Wrought Iron—Prussian Blue.
Steel—Carmine and Prussian Blue, mixed to give a purple shade.
Steel Casting—Same as the above darkened by Venetian Red.
Cast-Iron—Neutral Tint made of India Ink, indigo, mixed with a little carmine.
Brass—Gamboge or Chrome Yellow.