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.
Introduction. The commercial photographic worker of today is not limited to any one particular method or brand of paper for printing. In fact, the variety of processes is so great that the needs of any photographer may be fulfilled both as to the resulting effect and to the expense. Much less trouble is experienced (by the beginner at least) by the use of the ready sensitized papers, and generally they will prove more satisfactory than those sensitized by the photographer himself. With a little practice, however, it is possible to coat any paper with a solution sensitive to light and to print on it when dried. The number of processes and methods which may be employed is without limit, yet all require a certain amount of practice and experience in order that uniform results be secured.
50. The plain salted paper was one of the first to be put into practical use, and also one of the simplest processes to manipulate. Owing to its slight cost this process is especially adapted to commercial work when either great numbers of prints are required, or especially large ones. The most important consideration, if the results are to be permanent, is the selection of the paper. The paper must be pure and free from foreign substances which would act upon the various chemicals used in coating the paper and in producing the finished print. It is necessary to first coat the paper with a sizing and salting solution, which will make the surface of the paper non-porous. In other words, prepare the paper so that the sensitizing solution will not penetrate into the paper itself, but remain on the surface, and also that it may combine chemically with it to give tone and quality to the picture. After the paper has been sized and salted and allowed to dry, it is ready to be sensitized. After sensitizing it is again dried and is then ready for printing, toning and fixing in practically the same manner as any other printing-out paper.
51. Although any ordinary pure paper may be used, Whatman's hot pressed drawing paper will be found of excellent quality; yet, when obtainable the Saxe or Rives brand should be used. The paper should have a plain matt surface. Whatman's drawing paper is more desirable for large prints, as it is heavier and stiffer than either of the other brands.
52. Object of Salting- If the raw paper stock is simply floated on the sensitizing or silver bath, dried and printed, the resulting picture will be flat and appear sunken, and when toned and fixed the image would almost entirely disappear. This is due to the fact that the sensitizing solution has penetrated into the paper, and but a very small portion of the silver salts have remained upon the surface to receive the direct action of the sunlight. It is, therefore, necessary that the paper be sized or coated with a solution which will keep the sensitizing bath from penetrating into the paper. In other words, the pores of the paper must be filled with some solution for two reasons: First, to keep the image on the surface of the paper; second, that it may combine chemically with the sensitizing solution and thus assist in giving quality and tone to the picture.