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Reilly, James M. The Albumen & Salted Paper Book: The history and practice of photographic printing, 1840-1895. Light Impressions Corporation. Rochester, 1980.


Chapter One
Basic Principles

There can be no doubt that for purely practical reasons the use of silver printing-out papers has greatly diminished in favor of develop-out papers. Yet printing-out papers will always be valued by those who seek higher image quality in the sense of fine execution and tonality, because in these things some kinds of printing-out papers--and I cite the albumen print as an example--have never been surpassed

--Fritz Wentzel, 19271

Printing with Silver Salts

The processes described in this book are all based on the fact that salts of silver are light-sensitive--that is, they chemically dissociate and form particles of silver metal in the presence of light energy. Silver salts have provided the basis for most photographic materials over the entire course of photographic history. Many other light-sensitive substances are known, and many of them--notably iron, platinum and chromium salts, as well as recently discovered photosensitive polymers--serve as the foundation for useful photographic printing materials, but all these systems lack the versatility of silver salts. Used singly or in combination, compounds of silver can produce a great variety of negative and positive images.

There are two large families or evolutionary strains of silver printing papers, differentiated by the way in which the image is formed. Most modern photographic papers belong to the class of materials known as develop-out papers, which means that the image is formed by the chemical reduction of silver particles after a brief exposure to light. Of course, all practical negative materials have been of the develop-out variety, since the chief advantage of this approach is that only a small amount of light energy is needed to create the image. Less well known is the fact that only since about 1905 have most printing papers been of the develop-out variety.

Printing-Out Papers

For the first 65 years of photographic history the chief method of producing prints was by means of the printing-out processes, wherein the image is formed by the action of light energy alone, without chemical development. Obviously, more light energy is needed than with develop-out materials, in some cases 100,000 times more. Historically, this meant that for printing-out papers daylight was the only practical light source, and even now it remains the cheapest and most satisfactory source in cases where mass production is not required. Printing-out papers are almost unknown today but they are still sold for the purpose of obtaining quick proofs of portrait negatives, though even this application is dwindling as color continues to grow in importance in the photographic industry.

illustration

Fig. 1. Checking the progress of exposure. Half of the hinged back of the printing frame is open, while the other half is still closed to maintain registration of the print and the negative.

Printing-out papers possess the advantage that because the image appears during exposure, the progress of exposure may be checked visually and stopped at the right moment. Another advantage of printing-out papers is that they have a very long tonal range, and can successfully reproduce detail from negatives of greater density range than develop-out papers can. In general, negatives that produce good prints on printing-out papers are too contrasty for even the "softest" grades of develop-out papers. The biggest disadvantage of printing-out papers from the modern point of view is their inability to produce prints by enlargement; the amount of light energy required to enlarge onto printing-out papers is enormous and impractical, so all prints must be made by contact.

CLASSIFICATION OF PRINTING-OUT PAPERS

Within the large class of printing-out papers there are two smaller classes or subdivisions--emulsion papers and salted papers. The differences between them come from the way in which the paper is tendered light sensitive, although both kinds depend on the same light sensitive substance, silver chloride. Salted papers are made in a two-step process whereby the "salt" (usually ammonium or sodium chloride) is first applied to the paper and then converted to silver chloride by a treatment with silver nitrate solution. Emulsion papers are made by a one-step process of coating the paper with silver chloride already formed and dispersed in an emulsion. The making and coating of emulsions is best done by machine, although it is possible to produce emulsion papers by hand on a small scale. The salted papers are eminently more practical to produce on a small scale basis, however, and are capable of a widely varied range of effects, textures, colors, and contrasts.

This book is about papers that belong to the category of salted papers, using the term in its technical sense defined above. The term "salted paper" can thus be taken to mean any handmade silver chloride printing-out paper made in two steps, a "salting" step and a sensitizing step. The fact that the two operations of salting and sensitizing are separate allows a much wider choice of materials to be used as a "binder" in which to disperse the silver chloride and keep the image on the surface of the paper. Many materials, most notably albumen, are unsuitable for emulsion-making yet are useful for salted papers. It is necessary here to mention that although albumen paper is a salted paper in the technical sense of the term, most people reserve the term "salted paper" to describe any handmade silver printing-out paper other than albumen paper. This ambiguity has arisen because albumen paper has such towering historical importance that it is usually talked about separately from all other salted papers, though it does actually belong to that class of materials.

CHARACTERISTICS OF PRINTING-OUT PAPERS

The characteristics of printing-out papers of all kinds differ greatly from those of develop-out materials. The most obvious difference is that of image color. While developed images generally are black (sometimes with a greenish or bluish cast), the color of printing-out papers after fixation is usually yellowish or reddish brown. To most people the color of fixed printing-out papers is not pleasant or agreeable, so a toning process is usually carried out prior to fixing, which alters the color to brown, purplish brown, purple, or black. It is the basic mechanism of image formation in printing-out papers which is responsible for their color. When silver chloride is acted upon by light, it dissociates into its component parts of silver and chlorine, and a tiny particle of metallic silver is formed. These tiny particles form larger aggregate particles that do not exceed a certain size, and which are relatively much smaller than the filaments of silver that are generated in develop-out papers by the action of the developing agent.

The aggregate silver particles that are formed in printing-out papers are of a size that chemists call colloidal, which means that they have special properties with respect to light. The particles are not large enough to absorb all wavelengths of light and thus appear black. Instead they absorb some wavelengths but not others, depending in part on the index of refraction of the material in which the particles are dispersed. In practical terms this means two things: first, different binders or vehicles used to carry the image, such as albumen, gelatin, or starch, will produce prints of different colors. Second, when the print is fixed, the color will change dramatically, since by dissolving the unreduced silver chloride present in the light-sensitive coating the index of refraction of the whole system will be changed, and the silver particles will be "packed" together more closely. These are the reasons why prints which have a rich purple or brown color after exposure change to a reddish or yellowish brown in the fixing bath. After drying the prints again change color, becoming darker and colder in tone because the index of refraction of the system and the distances between particles have changed, thus affecting which wavelengths of light are absorbed. The fact that the colloidal silver image changes color depending on the nature of the vehicle or binder material used on the paper constitutes some means of controlling print color, but the toning process plays a greater role and provides more possibilities for control.

SILVER CHLORIDE

As stated above, it is light energy alone that reduces the silver salts to metallic silver and thus forms the image in printing-out papers. While many compounds of silver exhibit the print-out property, the most useful for printing papers is silver chloride. Silver chloride is insoluble in water and in most solvents, so it cannot simply be brushed on to make photographic paper. It must be formed in place by a process of first treating the paper with a soluble chloride like sodium chloride--table salt--and then treating it again with a solution of silver nitrate. The two chemicals react, forming silver chloride and sodium nitrate, the latter of which takes no role in forming the image and either dissolves into the silver solution or is washed away in processing.

Pure silver chloride paper is unsatisfactory for printing purposes because it produces gray and flat images. Successful printing with silver chloride depends on the presence of two additional factors: "active" organic substances and excess silver nitrate. Both of these are needed to impart adequate sensitivity and a rich appearance to printing-out papers. It was William Henry Fox Talbot, the inventor of negative-positive photography, who first realized the critical relationship between the relative amounts of chloride and silver nitrate. He found that when chloride and silver nitrate were present in equal amounts his papers were hardly light-sensitive at all, compared to when silver nitrate was present in great excess. Talbot found that about six times more nitrate was necessary and established that the "salting" solution should be 2-4% in strength and the silver nitrate 12%. The reason why so much silver nitrate is necessary was explained by the great 19th-century photochemist Hermann Vogel, who reasoned that as light energy dissociates each unit of silver chloride, the chlorine that is liberated simply unites with the silver nitrate present to form new silver chloride. Light breaks down this newly formed silver chloride, and the cycle begins again, to be repeated over and over. When excess silver nitrate is available, more image silver will be formed and a greater maximum density attained.

THE ROLE OF ORGANIC BINDERS

Experience has shown that certain organic substances have a very favorable effect on image formation in printing-out papers, and these may be designated "active" organic substances. The most important are albumen, gelatin, and organic acids, such as citric, tartaric, and oxalic acid. These "active" organic materials facilitate the more complete reduction of silver chloride and also themselves form light-sensitive substances when in contact with silver nitrate (silver albumenate, silver citrate, etc.). There are many other organic substances used for printing-out papers which are not "active" in the same way, that is, they do not facilitate more complete reduction of silver chloride, but definitely do make a contribution to the printing paper by keeping the light-sensitive materials on the surface and preventing a dull "sunken in" appearance. The most useful of these substances is starch, although lactose, agar-agar, carageenan and resins have also been used for the purpose.

One of the most basic dynamics with any photographic paper is the location of the light-sensitive layer, that is, whether it is confined to the surface of the sheet or has penetrated deeply into the paper fibers. In the latter case the maximum density obtainable on the material will be lowered and the prints will have a matte surface, because the light reflected from the paper will be scattered and diffused by the paper fibers. If the image is produced in a compact layer resting on top of the paper fibers, this scattering is minimized and the maximum density obtainable is much greater. Also, if the light-sensitive coating is itself composed of some smooth and transparent substance like gelatin or albumen, the scattering of light in the white areas of the print will be minimized as well, and the paper will look more "brilliant" and have more contrast. All the various binder materials used in salted papers perform the function of preventing the penetration of the image layer into the paper fibers, although the results also depend on the nature and amount of binder used.

Another benefit of keeping the image on the paper surface is a gain in sharpness and capacity to render fine detail. The early history of printing papers shows a steady evolution of techniques for producing papers capable of greater resolution and contrast,fueled by a desire to reproduce the fine detail present in negatives on waxed paper and glass. Obviously the basic smoothness of the raw paper stock has a great effect on the resultant print, arid so does the amount of organic material coated onto the raw paper. Albumen, for example, may be applied in pure form to produce a glossy paper or may be diluted to any strength, with a corresponding loss of gloss, detail, and "brilliance" of image.

illustration

Fig. 2. The would-be photographer confronts his textbook and chemicals. From a 1903 advertisement.

Relating Theory to Practice

The terminology and basic theoretical considerations described above are, of course, not enough to carry out the practice of making albumen and salted papers, but they do form a framework in which to begin work. The historical literature abounds with recipes for all sorts of salted papers, including some with very exotic ingredients and procedures. With patience and care, most of them will "work." The difficult part at first is relating theory to practice, and persevering until the true cause of a difficulty becomes evident. Most of the problems that beginning printers encounter are not the result of defective formulae, but of difficulties in coating techniques.

With whatever sort of paper is desired--albumen, arrowroot, etc.--it will be necessary to get a "feel" for the exact method and amount of coating that will produce the best results. Also, coating methods which seem effortless for one person may be totally unworkable for another. For beginners, it is best to trust the formulae as given, and focus on striving for rich, even coatings. Do not be afraid to try out new ideas for coating methods. Once a "feel" for the basic materials and coating methods is established, it is then possible to create variations on formulae and fulfill the promise of creative expression with a totally unique photographic material.

The key to success in every operation described in this book is clean and careful work. Because of the presence of excess silver nitrate, the printing-out papers are far more subject to damage from careless handling and contamination than are modern photographic papers. Contamination is a very real danger, and only good housekeeping practices will prevent it. Failure to clean up spills will load the air in work areas with chemical dust, and uncleaned trays will surely cause stains in prints. A thorough and careful approach to housekeeping in work areas is actually part of a whole attitude that leads to good results. This attitude is one of patience and care, and a thoughtful attention to detail. Success will come through a process of slow refinement of results and not through discovering the one "right" formula. A system of record keeping is essential, both to obtain repeatable results and to understand the causes of problems.

Any work with the methods described in this book will help to make a direct link with a photographic tradition from which "convenience products" in photographic materials have made us very distant. Respect and understanding for the achievements of early photographers cannot help but grow from acquaintance with their methods.


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