CHAPTER II.HALF-TONE INTAGLIOS.
We now come to quite a different class of work, namely, the production of half-tone intaglio plates. They may be produced in many ways, each way giving results quite unlike the others.
The first process is based on the half-tone method given for typographic blocks, modified to suit intaglio.
In this, as in fact withALLmethods, we must first of all produce a satisfactory transparency. That is best done by reproducing in an enlarging camera.
Place the negative, with the subject masked with tin-foil, in the window, then focus upon the ground-glass screen of the camera the requisite size; then prepare a wet collodion plate, and, having fixed a grained screen* in front of the carrier, put the plate in its place, then expose to the light and develop as directed for wet collodion pictures; the result, however, will be a positive and not a negative, and instead of the grain being interspersed through the high lights, the shadows will be grained.
* The grained screen is a copy from a proof from a fine ruled copper plate. See Chapter on “Half-tone Blocks on Zinc.”
* The grained screen is a copy from a proof from a fine ruled copper plate. See Chapter on “Half-tone Blocks on Zinc.”
The transparency must be made in this manner—i. e., from an ordinary negative with a screen in front of the sensitive plate, so that the shadows and half tones are grained or broken up. This would not be the case if the transparency was made from a negative grained for the production of a type block, as in such a negative the blacks are represented solid and the lights and half-tones grained should be made on large sized plates.
The transparency made must fulfil all the conditions necessary for the production of type blocks—i. e., the film must be perfectly free from veil or fog; it may be varnished or not.
The mark put upon the negative from which the transparency is made, will cause the edges of the transparency to be quite clear. Coat a clean piece of polished copper with the bitumen solution, using the whirler as before; then{123}place the transparency in the printing frame, film up, and place the bitumen coated copper plate in position, so that the image is quite in the centre of the plate: fasten the printing frame and expose to the light.
The exposure will, of course, vary according to the strength of the light, and should always, if possible, be made either in direct sunlight or by electric arc light.
The development is effected by immersion in turpentine, and with the washing and drying, has already been described.
The image on the copper plate being satisfactory, it may be retouched, if necessary, then immersed in either of the etching fluids described in the last chapter.
Rebiting, if necessary, may be done after rolling up with the resist ink there given, but care must be taken in this rebiting to guard against interfering with the grain of the plate.