might impair the balance of the tones on the printed page. Shadow dots are especially desirable when the plates are to be stereotyped.

If the shadow dots (B) on the negative, Fig. 19, No. 2, are too large, the print made from the completed engraving will be too gray in the shadows. They will result in a flat, contrastless halftone picture.

In

In Fig. 20, is shown a picture under two treatments. preparing the halftone negative for No. 1, the shadow dots were dispensed with entirely. The shadows in this picture

Fig. 20-A halftone without and with shadow dots (60-line screen). yield a jet black tone entirely unrelieved by white dots. In No. 2, the shadow dots were made large on the negative. The resulting picture printed from the plate is gray in the shadows. A better reproduction of this picture would have shown the shadows not so black as in No. 1, nor so gray as in No. 2. The engraver can regulate the amount of contrast to a considerable extent, although the tones of the original photograph limit him. For instance, it may be possible for him to make a slight increase in contrast in reproducing an extremely gray photograph, but he may not be able to make it into an engraving that will print a picture with well-balanced tones.

When the sensitized metal has been exposed in the print

ing frame sufficiently long, it is removed and held under running water. The soluble parts of the coating are washed away from the metal. Heat is then applied to harden the enamel, after which the plate is ready for the etching bath. Acid in a rocking tub is dashed back and forth across the face of the plate until the open parts of the metal are eaten down, leaving the enamel dots standing in relief.

The form and area of the dots undergo a change during the etch. Fig. 21, No. 1, represents in the upper left corner (A) the enamel dots in the high-lights before the etch begins. As the etch A progresses the acid eats downward and laterally. The lateral action of the acid decreases the diameter of the dots by undercutting the enamel-protected surface, leaving an umbrella-like fringe. When this fringe is broken off by brushing, the enamel dots (now in relief) have A the appearance of the dots in Fig 21, No. 2, upper left corner (A).

It is highly important that the enameled dots in No. 1, A, be as large as possible without being connected at the corners, else the dots would reduce in diameter and finally disappear before sufficient depth had been attained in the etch (No. 2, A).

1.

B

2.

In the lower right corner (B), No. 1, is represented the small openings of the enamel in the shadows. When the plate is etched (B), No. 2, these openings have an increased diameter as well as depth.

RE-ETCHING

It frequently happens that after a halftone plate has been etched as far as the dots in certain places may stand, other

Fig. 22-A halftone "flat-etched" (A), and re-etched (B).

(120-line screen)

parts of the surface may need further etching. This is often the case in reproducing a flat or an over-"contrasty" picture.

When the copy is flat and contrastless, re-etching will give brilliance to the high-lights and shadows. Details in the shadows may be brought out by re-etching an over-"contrasty" plate.

Re-etching consists in painting out with acid-proof varnish the parts that are etched enough and in returning the plate to the etching bath. The plate may be removed from

the acid and parts may be painted out again, preparatory to a third etch, and so on, until the relations of the tones on the plate are improved. Between etches the plate-maker may clean the surface of the plate and rub a white powder (magnesia) into the crevices between the dots to determine the condition of the plate.

After the final etch the edges of the plate are beveled or rabbeted by a power machine in order to provide space for nailing the metal to the wooden backing. The mounted plate is then planed on the edges and back (if more than type-high). It is now ready for the printer.

Fig. 23 (A) Pen decoration with silhouette for halftone insert. (B) A combination line and halftone picture (85-line screen).

COMBINATION OF LINE AND HALFTONE

Combinations of the two methods are represented most frequently by the halftone news picture and its surrounding line border design. The photo is first taken to the art de

partment, where a pen border design with silhouetted or blackened panels is drawn. The engraver makes a line negative from the drawing. Then he makes separate halftone negatives from the photographs. The line negative is then stripped and

into its transparent parts (corresponding to the silhouettes or black panels of the drawing) are inserted the halftone negative films, which are made of such a size as to fit exactly into the transparent parts of the line negative. The print is then made from the negative onto the metal and etched. When the halftone part of the plate is etched sufficiently deep, it is