With complex drawings it is often difficult to tell whether the lettering and figures are of large enough size to be read easily after they are reduced to the size to be used for printing. By looking through a reducing glass it can be determined at once whether the drawing is in correct proportions. A reducing glass is similar in appearance to the ordinary magnifying glass, but the lens is ground concave instead of convex so that everything seen through the glass appears of smaller size. The ordinary reducing glass can be

330 GRAPHIC METHODS

used for a reduction through quite a range of different sizes by holding the glass at different distances from the drawing which is being considered.

One of the commonest errors made by the beginner in preparing charts from which printing plates are to be made is that he does not allow for the reduction in widths of the various lines. If the printing plate is to be made one-third the lineal dimension of the original drawing, it is essential that the lines on the original drawing should be made three times as wide as they are to appear when printed. The novice will find that even though he uses a reducing glass with great care, his heavy lines will at first nearly always appear less wide and black than he had expected and hoped that they would be.

Quite often it is desired to change the proportions of some chart so that the ratio between height and width may be different from that of the original drawing. Though the photographic process used in the photostat machine or by the engraver (in making plates for printing) permits a change in size, the same proportions remain between width and height. There would seem to be enough demand to justify an engraver making a combination of lenses by which one dimension of a drawing may be changed more than the other dimension.