The American Printer: A Manual of Typography / Containing practical directions for managing all departments of a printing office, as well as complete instructions for apprentices; with several useful tables, numerous schemes for imposing forms in every variety, hints to authors, etc.

by Thomas MacKellar

PHOTO-ENGRAVING.

Photo-engravings are produced by means of photography. It is a fact worthy of note that experiments in photographic engraving gave rise to photography itself. The aim of Nicéphore Niepce, when he began his researches in 1813, was not only to fix the image obtained by the camera obscura on a plate of metal, but to convert this plate into an engraving which could be used on a printing-press. His early death prevented his perfecting the process to which he had devoted much time and study.

Three distinct methods of photo-engraving are employed in the United States, viz.: swelled gelatine, photo-etching, and wash-out. The latter is known as photo-electrotyping.

The first steps to produce a plate by any of these processes are exactly alike, i. e. a perfectly sharp negative, either in line or stipple, must be produced. If the copy furnished is a wood-cut, steel or lithographic print, in which the lines are absolutely black on white paper or card, the negative is made direct and no drawing is necessary, unless a very great reduction is required, when it becomes necessary to make a drawing, the lines of which are made open enough to stand the necessary reduction. Where the copy furnished is a photograph, or wash drawing, it is first photographed one half larger, or, where fine work is desired, twice the size the plate required. In cases where exceptionally fine work is required it is even made three times the size. The photograph thus obtained is technically termed a silver print, and is an untoned print on plain paper. On this silver print the artist makes his drawing, using the best India ink, which must be so black that the finest hair-line, when examined through a magnifying glass, appears absolutely jet black. After the drawing is made, an alcoholic solution of bichloride of mercury is poured over it, and quickly washed under the tap, leaving the drawing on perfectly white paper. The artist then does whatever retouching may be necessary, and the drawing is ready to be photographed. The advantages of this method of drawing are apparent. The artist, being able to work directly on the enlarged photograph of the object, obtains absolutely correct outlines and detail. The drawing, when finished, is sent to the gallery, where it is photographed to the required size of the plate. The focus of the camera is carefully adjusted with the aid of a focusing glass, so that the negative resulting will be perfectly sharp. This must be carefully done, for unless the negative be sharp a perfect plate cannot be obtained by any process. The sensitized collodion plate is exposed in the camera from one to six minutes, after which it is taken again to the dark room, developed, and fixed. It is then intensified until the portions representing the whites of the picture are perfectly opaque. Up to this point all the processes are alike, and the differences from here will be noted.

If the plate is to be produced by the swelled gelatine process, the negative is varnished and sent to the gelatine room. Here the gelatine is dissolved and the sensitized solution of bichromate of potash is added, and it is flowed on plate glass, then placed in a drying box, where a current of air is continually passed over it. When the gelatine is dry it is placed in a printing frame, in close contact with the negative, and exposed to the light. On removing the negative the picture is plainly seen on the gelatine, the action of the light having changed the color of the exposed portions of the gelatine, besides rendering those parts insoluble, while the parts protected from the action of the light, by the opacity of the negative, remain soluble, and are swelled up by immersion in cold water. The gelatine is then an exact opposite of the plate, the whites being represented by the raised portions. From this mould, or relief, a cast is made in a preparation of wax or plaster, when it is ready for the stereotyper.

For the wash-out or photo-electrotype process, the negative, when dry, is not varnished, but is first coated with a rubber solution and then with plain collodion, after which it is immersed in a dish of acetic acid for about five minutes, when it is stripped from the glass and turned over. It is then what is termed a reversed negative. The method of preparing the gelatine is very much the same as for the swelled process, with the exception that it is cooked for about forty-eight hours, and with the addition of several preparations which are introduced at the time of sensitizing, to make it easily washed out. The negative is exposed in the same manner as described before, but the time of exposure is generally less. After being taken from the printing frame the gelatine is gently scrubbed with a line brush, and kept in tepid water until a very slight relief is obtained. It is then immersed in alcohol for a few seconds, and dried with a cloth, when it is covered with a preparation of lamp black and glycerine, which is allowed to remain about five minutes, when the surface of the plate is carefully rubbed with clean muslin, exposing the surface of the lines,—all this being done in a dark room before an orange light, which is non-actinic. The gelatine is now placed in a frame and exposed to the light from five to twenty minutes, the lampblack protecting the spaces between the lines from the action of the light, so that those portions remain soluble. The gelatine is again scrubbed until the proper relief is obtained, after which it is allowed to dry for about twelve hours, when it becomes hard and is ready to be electrotyped.

The negatives for photo-etching are stripped and reversed in the same manner as for the wash-out process. The metal generally employed for this process is zinc, though copper is sometimes used for very fine work. The zinc is very highly polished, and a thin sensitizing solution is flowed over it and dried, after which it is exposed under the negative to the action of the light. It is then rolled up with lithographic ink, placed in a dish of cold water, and gently rubbed with absorbent cotton, the ink readily leaving the unexposed parts, but remaining on the exposed lines or dots. It is then quickly dried and dusted over with dragon’s-blood powder, which adheres only to the remaining inked portions. The plate is then heated and cooled, and is ready for the etching bath, which consists of a small portion of nitric acid and water. After the first bite the plate is again powdered, heated and cooled, and more acid added to the bath. This is repeated several times, after which the plate is ready for the press. The sides of the lines are protected by the manner in which the powder is applied after the first bite. The relief obtained in this way is greater than can be obtained by any other process.

In reviewing the three processes above described, it is readily seen that the photo-etching process is the shorter method, no moulding or casting being necessary, and the sharpness of the finest lines is preserved in a manner impossible by the other methods. The plates are much deeper, and are equally suitable for the finest art work, down to the roughest newspaper work. This process, of which there are several modes of operating, has become very popular in the last few years, owing to the many improvements introduced by the process inventors, who have turned their attention to it. It has many advantages, among which is the fact that a plate can be put on the press within two hours from the time the copy is ready; and the wearing capacity of the plates is greater. By this process more than 300,000 impressions have been taken from plates of fine work, while swelled gelatine plates of the same character of work would not stand over 5000, and electrotypes 50,000 impressions. The main advantage of photo-etchings to the printer is, that the plates do not require constant washing up, as is the case with plates made by the other processes.

A photograph, brush drawing, or any copy that is not made up of line or stipple, can be produced without the necessity of a line drawing by the aid of the half-tone process. There are several of these processes in operation in this country; and, although originally introduced in Germany by Miesenbach, it has been so improved by American inventors that the European work is far below the standard of the United States. The principal methods of half-tone in this country are worked secretly by the inventors, each having modifications and improvements of his own. It is impossible to give a thorough description here, as none of the inventors are willing to risk patenting their processes, and a complete publication is not desirable. The copy is first photographed, giving a negative with all the details of the original. This negative is then exposed to the camera, and the result is a positive, or, as commonly called, a transparency. This positive is then placed in contact with a glass plate covered with ruled lines. This plate is termed a grating. Being placed in contact, they are then photographed together, giving a negative of the object made up of lines and dots, representing the lights and shades of the picture. Here the half-tone process ends, the resulting plate being produced by any of the photo-engraving methods; but the most satisfactory results are obtained by photo-etching. The main objection to the half-tone plates is their lack of relief. No great depth can be obtained without sacrificing the effect. In printing these plates the greatest care in making ready must be exercised, and a smooth surface paper must be used. It is also necessary that a fine grade of ink be used in small quantity, and that it should be properly distributed.