This method of making transparencies in the camera yields the best possible results, as the rays of light are projected by the lens perfectly parallel, and the resulting picture is far crisper than it is possible to obtain by exposing in the ordinary manner.
If the negative to be reproduced is already made, and is larger than required, mask the margin by means of the tin-foil, place it in the holder of an enlarging camera, film towards the lens if the negative was made without a mirror; but if the mirror was used and the negative is a reversed one, the film must be placed away from the lens.
The camera is now adjusted so as to get the image the size required, then a sensitive wet collodion plate is used to receive that image and produce the transparency.
The transparency for printing upon a copper plate must, when laid upon a piece of white paper, allow every detail, however minute, to be perfectly distinct by reflected light. If this is not so it will be impossible to get a good engraving on the copper plate.
The transparency being secured, a plate of highly polished copper is cleaned with a little fine whiting and alcohol, then flooded with water. Take care that all grease has been removed (which will be detected by the water running in streaks); next wipe the plate carefully with a clean, soft cloth, and place it in the jaws of the whirler mentioned in the chapter on the apparatus for zinc printing. In the dark-room coat the copper plate with prepared bitumen (see chapter on engraving on zinc in half-tone), and set the whirler in motion. When the film of bitumen is dry, place it in contact with the transparency in a printing frame, and expose it to the light (sunlight, if possible).
The time of exposure will depend very greatly upon the time of year and day, but, in direct sunlight, ten to fifteen minutes will be about the time.
After exposure, the copper plate is removed from the frame, and placed in a dish containing turpentine. Keep it rocking until the image is developed by the unaltered bitumen being washed away, then remove the plate from the dish, {121} and wash it well under the tap. When quite dry, coat the back and edges of the copper with ordinary black varnish laid on with a camel’s-hair brush, so as to prevent the mordant to be used from attacking the back.
Alterations and additions may now be made by means of transfer ink thinned with turpentine, applied by a sable brush, or by means of an etching needle or scraper, remembering that the etching needle or scraper will make a black line and the transfer ink will cause a white mark, or exactly the reverse of a type block. The plate is now ready for etching in a
| Saturated solution of Perchloride of Iron | 2 | ounces. |
| Water | 10 | ounces. |
Use a porcelain dish for the solution. Immerse the plate, and keep it rocking for about ten or fifteen minutes, then remove it, and wash it under the tap, rubbing it gently with cotton-wool. After drying it, warm it slightly, then roll up with a glazed leather roller, or a smooth India-rubber roller charged with the hard ink used during the clearing-up of the zinc block, viz.: