Photo-engraving, Photo-etching and Photo-lithography in Line and Half-tone / Also Collotype and Heliotype

by W. T. Wilkinson

Fig. 5.

For the production of these enlarged transparencies, an enlarging camera will be required, which may be provided by having an arrangement in front of the ordinary camera, fitted like the accompanying figure, consisting of two boxes, one sliding within the other, the negative from which the transparency is to be made being placed in a carrier at B.

In the illustration the sides are shown open, but only for simplicity, as they must be quite opaque. In using such an arrangement, the camera must be brought under the skylight of the studio, and the light reflected through the negative, by placing a large sheet of white paper at an angle of forty-five degrees in front of the negative.

Another and perhaps better method will be to cut a hole in a dark-room at a proper height for the camera, and fix the negative in the hole, then adjust the focus upon the screen, illuminating the negative by means of a reflector fixed at an angle of forty-five degrees.

The transparency being secured, it is varnished, and all blemishes or spots removed by means of a sable brush, and a little carmine color; it is then placed in contact with a suitable screen, and the two together are inserted in the {68} place previously occupied by the original negative. Now adjust the camera so as to get the image on the focussing screen the proper size, and proceed to make a grained negative by the wet collodion process exactly as described in Chapter II., Part I., and above. When a negative containing all the details of the original negative broken up by the fine grain of the screen is obtained, it may be dried and varnished, and then it is ready for printing upon the zinc.

All pinholes, etc., should be stopped by means of a fine sable brush and Indian ink. The printing on the zinc should be done by the bitumen process, Chapter VI., Part I., as the albumen is not nearly so perfect. If, however, the albumen process be preferred, the printing is done in the same way as described in Chapter V., but extra care must be taken, first, that the zinc plate is thoroughly and evenly polished; secondly, that the graining bath is kept weak with plenty of alum in, so as to have the grain on the plate as fine as possible; thirdly, that no speck of dust, dirt, or any air-bubbles be on the film after coating, and that the whirling be effectually done so as to get the sensitive coating as even as possible.

The inking up requires no comment, as it must be done as evenly and thinly as possible, for both line and half-tone.

In development, a little more energetic friction will be necessary, but extreme care must be taken not to abrade the ink surface. Continue the rubbing until all the details are developed, and bear in mind that the finished block will be exactly like the zinc after development.

In printing these half-tone zincs, it often happens (like printing in silver) that to get the best results some portions will require less exposure than others. The best way to stop back any portion or portions, is to cover the front glass of the printing frame with whiting mixed with water to the consistency of thick cream; apply with a rag over the places in the negative, before exposing to light, and at the end of one-third, or in case of very deep shades, one-half the exposure, clean off the whiting and finish the exposure without any obstruction to the light.

The exposure to a grained half-tone negative will be one-half to double as long as a simple line negative.