Chapter 2
Coated Printing Paper

This chapter discusses albumen, collodion, and gelatin paper prints, and baryta undercoating.

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The salt prints made from calotype negatives were the first successful paper prints, but several problems prevented wide-spread international acceptance comparable to that of the Daguerreotype, even though calotypes were often larger and could be reproduced. One problem was the litigious personality of Fox Talbot, who constantly engaged in lawsuits over the use of his patents, attempting to broaden his claims to include all sorts of improvements by himself as well as others. In fairness, many other inventors of the times did the same thing, in some cases hindering the public acceptance of their processes.

Another problem was the lack of sharpness caused by printing through the paper fibers in the negative, even though it was alleviated by waxing the negative. In addition, salt prints were soon found to be susceptible to rather rapid fading, which did not afflict Daguerreotypes.

Image sharpness in salt prints was also adversely affected by penetration of silver salts into the fiber structure. If the paper was totally immersed in sensitizing solution, light scattering in the paper caused darkening and ghost images on the back of the print and an unacceptable degree of blurring. For this reason sensitizing was always done by floating the paper on one side only; sizing the paper with starch or glue also helped reduce penetration of chemical solutions in the paper.

To some people the slightly soft appearance of a salt print was pleasing, but then, as now, many people wanted glossy sharpness. Today all printing papers are comprised of several coated layers on flexible bases, most of them on synthetic films or resin-fiber composites rather than on plain paper.

Collodion, albumen, and gelatin, the same materials eventually used on glass, were tried on papers and all three were eventually successful in varying degrees. Printing papers did not have to be as sensitive as negative materials for cameras, nor were keeping qualities as critical. Coatings tended to stick to paper better than glass, and formulations were modified for the two bases.

Albumen: 1848 - 1890's
Experiments with albumen on glass apparently preceded those on paper. In 1847 the Frenchman Niepce de Saint-Victor published a process consisting of albumen on glass, but the sensitivity was low. In 1850 the Frenchman Louis Desire Blanquart Evrard announced his albumen printing-out paper process, which dominated photography for forty years. Printing-out paper is discussed in Chapter 2.

'Albumen' is chicken egg white, and many were the recipes for concocting the most sensitive and best appearing coatings. There were also recipes for using the left-over egg yolks, which according to Newhall totaled an estimated 20 million in one year. Leather tanneries helped by consuming the surplus yolks.

Albumen prints were generally sharp and glossy, in contrast to the soft matte appearance of calotypes. Some matte albumen paper was made by adding starch to the albumen, but glossy predominated. After the mid 1870's albumen paper was given extra gloss by roller-burnishing; microscopic examination can sometimes reveal the faint eggshell texture of non-burnished emulsion and infer its period. The microscope will often reveal cracks and fissures in the coating caused by expansion stresses from the mounting.

Arguments over matte-versus-glossy aroused strong differences of opinion. Albumen paper had a more durable surface than salt prints, an important advantage on the increasingly popular cartes de visite and stereographs. Pre-salted albumen paper was made commercially in rolls up to 33 inches wide, ready for silver nitrate sensitizing by the user. It was variously salted with sodium chloride, ammonium chloride, and potassium chloride or bromide. There were conflicting notions about the efficacy of these materials: sensitivity and keeping qualities were important criteria. But sensitized albumen paper did not retain its sensitivity in storage and had to be sensitized by the user just before exposure.

The albumen solution was coated directly onto the sized paper base. Since baryta undercoating was not used until the mid 1880's, paper fibers are visible through the albumen in the highlights. In the shadows the fibers usually cannot be seen because of image density. Although the fibers can be seen (some magnification may be needed), the fibers are not exposed as they are in the highlights of carbon prints. Examination under a microscope reveals the difference; in an albumen print the top surface of the albumen first comes into focus smooth and glossy, with the fibers under the surface.

Albumen prints were often gold-toned to alleviate the fading problem, producing a characteristic purple-brown color. This is the typical color of surviving 19th century photographs, the majority of which (estimated to be 90%) are albumen prints. They are sometimes called 'sepia' but that is a misnomer and, in fact, a different process. Figure 1a is a black and white reproduction of a typical faded albumen low-contrast print; Figure 1b is a print of the same subject that was gold-toned to a chocolate brown.

Black and white reproduction of faded albumen low-contrast print Print gold-toned to a chocolate brown
Figure 1a Figure 1b

    

Albumen paper was the first photographic paper manufactured on a large scale. Daguerreotypes were too expensive for the mass market, and calotypes were involved in too much litigation. Since the demand for paper was so large, it became commercially feasible to devote some effort to tailoring the quality of the paper base to the peculiar needs of photography. All-rag content was a necessity, and bits of buttons and metal caused glaring defects. Chemical trace impurities caused longer-term problems of spots and fading. Two European firms, one Belgian and one French, eventually emerged as the dominant world-wide suppliers.

Paper stock for albumen prints was made in more than one thickness, but most of it was dense, smooth, thin paper about the thickness of modern twenty-pound computer or copy paper. This is little more than half the thickness of modern single weight photo papers and only one fourth that of double weight. Thin paper was used because it was easier to manipulate during the sensitizing flotation operation. Thin paper was also easier to glue to carte de visite and stereograph cards, which represented the largest market for many years: nearly all albumen prints were mounted.

Reilly's 1980 book [121] is the definitive reference for albumen prints, but descriptions are found in most histories. Bernard [22], Eastman Kodak [47] and [122], George Eastman House (F), and Holme [77] are especially useful because of their full color reproductions.

Collodion Paper: 1867 - 1890's
The first industrial production of collodion-coated paper was in 1867 by J.B. Obernetter in Germany. It was a silver chloride printing-out paper coated by hand until 1889 when machine coating was introduced, incorporating a baryta layer. Both glossy and matte surfaces were made available.

Collodion is a solution of gun cotton in ether and alcohol; it had been used in surgical applications and is very flammable. It does not react chemically with silver salts as albumen and gelatin do, and was more stable than albumen, but fading is related to trace chemicals (intentional and otherwise) in such complicated ways that no blanket assertion is justified.

The use of collodion in the wet plate glass negative process had a much longer vogue than collodion-coated paper. A good description is found in Wentzel [151, 69-71]; Towler [145] has a very complete review of the processes; also see Newhall [105, 126] and Eder [48, 536].

Collodion papers were gradually phased out by the 1890's as the faster and more convenient gelatin papers became available.

Gelatin Papers: 1879 - present
Gelatin silver papers were made as chlorides, bromides, and chloro-bromides. The differences were in sensitivity and color tone, and in whether they were developing-out (DOP) or printing-out (POP) types.

Peter Mawdsley (England) suggested gelatin silver bromide paper in 1874 but it was not a commercial success. Sir Joseph Swan was more successful in 1879 and gelatin paper began to supplant albumen paper. By 1884 Eastman Kodak had a coating machine in production.

The first POP emulsion paper that produced a visible image without a negative (because it contained excess silver nitrate) was glossy collodion paper, and it enjoyed considerable popularity in the late 1880's. About 1890 Aristo paper was introduced; this also was a Printing Out Paper, and it is still in use as a studio proofing paper. Both POP papers were baryta-undercoated.

Developing-out gelatin silver chloride paper was invented by Eder and Pizzighelli in 1881 in Austria, and was later manufactured as "Alpha" paper.

This was the period of the popular 'gaslight papers', which were fast enough to be exposed under gaslight instead of sunlight (which albumen paper required); they could then be developed and fixed by turning down the gas. They all had baryta subcoats. Gelatin silver-chloride paper was made in both printing-out and developing-out forms. Some other trade names were: Velox, a DOP chloride or chlorobromide; Solio, Ronex, and Seltona were POP chloride proofing papers.

When DOP gaslight papers were first introduced they represented the ultimate in sensitivity, but after the more sensitive bromide papers were introduced, gaslight papers were the slowest ones. Bromide papers became the choice for enlarging as they are today, while the slower chloride papers are generally used for contact printing.

The technology of paper processes changed very rapidly in the 1880's and 1890's as collodion and gelatin supplanted albumen. At the same time silver chloride and bromide in both POP and DOP versions competed, and it is difficult to state a simple time line for dating purposes as 'modern' manufacturing processes began to dominate around the turn of the century. Identifying the competing types of this period by simple inspection is very difficult. The illustrations in Reilly [122] are particularly helpful.

Matte papers
According to Eder, matte-surfaced bromide paper was produced as early as 1879 by using starch in the gelatin. Hubl added starch to albumen paper in 1895, a little late in its history. Another way of diminishing gloss was mechanical stippling. This produced minute indentations in the surface without penetrating it, and can readily be seen under a microscope. The earliest date of its use is unknown at this writing.

Tarnishing
This form of age deterioration is known by different authors as silvering, bronzing, and mirroring. The appearance is that of a metallic sheen of various colors, more prominent in the dark regions of the image, and eventually occurring in most silver images. The sheen can be very pronounced, almost like a mirror except that reflections are not specular.

It is most common in silver gelatin DOP images, but it can occur in other silver images in an organic binder, including nitrate negatives. It does not occur in binderless images such as salt prints and platinotypes. The cause is a change of state of the image silver by a complex process influenced by several factors, with the formation of metallic silver on the top layer. See Reilly [122] for a discussion of the phenomenon. The mechanism may not be identical in all cases, since the incidence of atmospheric sulfur, moisture, and processing residues vary. The effect is so obvious in nearly all glossy DOP images of that period that it can serve as an identifier. World War I - era pictures commonly show the effect.

Figure 2a shows a picture (dated 1905) in diffuse lighting; figure 2b shows the top of the same picture illuminated with light from the camera position; it shows heavy tarnishing. The same effect is apparent if the observer tilts the picture slightly in normal light.
References: Eastman Kodak [47, 15; 74; 132; 134]; Crawford [38, 65].

Picture (dated 1905) in diffuse lighting Illuminated with light from the camera position
Figure 2a Figure 2b
   
Baryta Coating

Baryta is barium sulfate, a white pigment with only a slight yellow tint. Coated on photographic paper under the sensitive layer, it functions as a smooth chemically inert coating that covers paper fibers and brightens highlights. The first description of baryta-coated paper appeared as early as 1826, before photographic applications were envisaged; it was finally patented in Paris in 1881. Manufacture of baryta-coated paper did not become widespread until the mid 1880's with the advent of machine coating. It therefore was not found in calotype or albumen prints; it did appear in machine- coated collodion and gelatin papers. Baryta was not hand applied by amateurs, so its presence indicates that the paper was commercially manufactured. Wentzel [151] has many intriguing details of baryta manufacture.

Baryta can be recognized in highlights where it completely hides the paper fiber. Barium can be identified nondestructively by x-ray fluorescence analysis, or destructively by wet chemical analysis.

Emulsion Identification

For identifying the type of emulsion, chemical or physical analysis can be used as discussed in Chapter 13. In most cases it is simpler to apply Rempel's solvent tests [124] to the emulsion. The solvents are distilled water and ethanol (reagent ethyl alcohol). Water swells gelatin but has no immediate effect on collodion or albumen, while alcohol dissolves collodion but does not affect gelatin or albumen. The tests may leave permanent marks and should be performed under a microscope on small marginal zones in non-image parts of the specimen. Reference 124 should be consulted for details.