This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
1. After a glass, or film, negative has been produced it is necessary to have some means of transferring the negative image to a positive form and placing it upon some permanent substance. For commercial purposes chemically pure paper is most generally employed, it being coated with a substance sensitive to the action of light. When this sensitive paper is placed under a negative, the light readily penetrates the transparent portions of the negative and causes a darkening of the sensitive chemicals on the surface of the paper. The most dense portions of the negative keep the light from acting upon the paper, so that when the shadows of the original object have become very dark, the highlights will be almost white, not having been affected to any degree by the light. There will, however, be not only dark and light spots, but a delicate range of gradation between these two extremes in exactly the same degree, but in reverse order, as they exist in the negative.
2. In the early days of photography there was no such thing as a prepared printing paper. It was necessary for the photographer to sensitize his own paper. The raw paper stock, being purchased with a coating of albumen on one side, was sensitized by floating it on a solution of silver salts. As this sensitized paper would keep for one day only, it was impractical to prepare more than enough for the day's work.
3. While this paper yielded most excellent and absolutely permanent results, the extremely tedious and troublesome manipulations necessary to prepare the paper for use, such as making up the sensitizing bath, sensitizing, drying and fuming the paper, etc., all entailed such a great deal of work, it made photography for the amateur almost prohibitive. Those who did stick to the work were compelled to employ professionals to finish from their negatives, and as few professionals cared to bother with amateur work, his pictures were usually slighted in the finishing. The constant cry for better results, or a more simplified process of printing, soon led to the manufacture of a ready-prepared product which could be manipulated by the nonprofessional. So today we have numerous papers, all giving different effects. The majority of these papers are good, and it is only a matter of judgment on the part of the photographer as to which surface and kind of paper is best suited to his quality of negatives.
4. The first ready sensitized papers manufactured, and that proved a revelation in their manipulation, over the old albumen process, were the collodion and gelatin papers. They supplied a high gloss surface and at one time were universally used by the photographic profession. Although many other processes have come into popular use since, the glossy paper is still indispensable for many commercial purposes. The principles involved in the manipulation of this paper are extremely simple and form the foundation for other printing processes.
5. Before entering upon the instruction for printing and toning of sensitized papers, it is necessary to have some idea of the chemical composition of sensitized printing-out papers. Without going into detail we will explain as follows:
6. It is first of all essential that the raw paper stock employed in the manufacture of these papers be chemically pure, as the paper supplies the foundation upon which the sensitive emulsion rests and any impurities in the raw stock will affect the emulsion to the extent that uniform and permanent results would be uncertain.
7. The manufacturer's first operation in preparing the raw paper stock is to size it, i. e., coat it with a substance that fills the pores of the paper and gives a good, smooth surface.
8. After the paper is sized, it is sensitized by coating with a solution of either collodion or gelatin, chloride of silver, and other chemicals which aid in preserving the emulsion. After being sensitized the paper is allowed to dry, when it is ready for use.
THE RETURNING HERD Study No. 1 (Frontispiece) By John M. Schreck.