The silver gelatin ‘monoculture’ has dominated photographic printing for nearly a century, but with each market-driven improvement the range of monochrome printing papers has become narrower. In the 1970s several artist-photographers began a rebellion against this hegemony by rediscovering some of the forgotten 19th-century processes which had lost the struggle for commercial viability. These ‘alternative’ printing materials generally require the hand coating of paper with solutions of light-sensitive chemicals. The aim is to broaden the spectrum of artistic photographic practice, ranging from the immaculately crafted platinum print with its exquisite ‘engraving black’ tones, on the one hand, to the painterly and sometimes flamboyantly coloured pigment images of gum bichromate, on the other. Alternative practitioners can select their materials and exercise manipulative control to a degree impossible with silver gelatin; or they can simply surrender, with wilful primitivism, to the serendipitous accidents of ill-defined photochemistry. Both holistic approaches can claim the satisfaction of being ‘true to one's materials’.
The wider movement known as ‘alternative photography’ also encompasses the revival of early camera processes (all silver halide based) such as the ambrotype, calotype, daguerreotype, pinhole, tintype, and wet- collodion process, and the accompanying silver-printing processes such as salted paper and albumen. This account, however, is confined to the ‘non-silver’ methods of making the positive print, which may be subdivided into three main areas of practice, according to whether their photochemistry requires salts of iron, or chromium, or purely organic substances. Aesthetic and practical considerations tend to cut across these subdivisions, and the permanence of the image substance is an important re-emerging issue for archives and the fine-art market, where the photographic print is viewed as art object sui generis.
Compared with silver gelatin printing, the conspicuous drawback of alternative processes is their low sensitivity to light—about a million times less than that of silver bromide enlarging papers. Projection printing on alternative materials is impossible with the technology commonly available, so contact printing is the only way to achieve a sufficient throughout of light; the final image can therefore only be the same size as the negative. This disadvantage was largely responsible for the early commercial demise of alternative processes such as platinotype, in the face of a growing market for miniature cameras and bromide enlarging papers.
The light source employed must be intense, usually with some ultraviolet content: the technologists tend to opt for mercury lamps, but the mystics prefer to sun-print in the time-honoured fashion—especially if they enjoy a good climate. One compensation for the insensitivity is that a darkroom with safe lighting is not required. Another, less obvious benefit is that these imaging systems are in principle capable of extremely high resolution; for instance, modern technology has rediscovered dichromated gelatin as an ideal material for recording holograms.
With low-sensitivity processes the easiest options are lensless: to make photograms of botanical specimens, fabrics, clichés-verre, or even the human form. If prints are to be made from camera negatives, the modus operandi must entail either a large-format camera, or enlarged internegatives, made in the darkroom or—increasingly—by computer technology. Although many kinds of substrate can be coated with alternative sensitizers, the usual choice is a fine-art paper selected from those intended for watercolourists, etchers, and printmakers, with regard to tint, surface texture, weight, and sizing; a few papermakers have recently introduced products especially suited for alternative photographic processes. To discover that paper can be a beautiful material may be a pleasant surprise for viewers inured to the bland surface gloss or mechanical stipple of the commercial silver gelatin photograph.
The class of alternative processes depending upon the photo-reduction of iron (III) was invented by Sir John Herschel in 1842. ‘Ferric’ salts of iron (III) with the ‘vegetable acids’— especially citric, tartaric, or oxalic acids—are sensitive to light, becoming reduced to ‘ferrous’ salts of iron (II) on exposure to the ultraviolet. Permanent images may be derived by further reaction of the product in three general ways. First, the iron (II) can reduce noble metal salts to the finely divided metal: platinum, palladium, and gold, giving rise to the platinotype, palladiotype, and chrysotype (or aurotype) processes; these are archivally permanent. Silver images can also be made by this indirect means; the processes called argentotype, argyrotype, brownprint, kallitype, sepiaprint, and vandyke, despite the variety of names, are all similar in principle, and have inferior prospects of permanence. Second, the iron (II) photoproduct may be reacted with potassium ferricyanide to give the powerful pigment Prussian blue (ferric ferrocyanide). Called cyanotypes, these blue images endure well, provided they are protected from alkali and excessive light. The third possibility is to couple the residual iron(III) with gallic or tannic acid, making iron-gall ink, the chief writing substance since the Middle Ages. Important once for photocopying, these ferrogallate, positive-working processes are no longer used.
All these iron-based processes are characterized by unmanipulated printing procedures, although they may be variously toned. Some provide a printout image, which can be inspected as it builds up during the exposure, using a hinged-back printing frame to retain registration. The need for test strips is thus avoided. Printout processes have the added benefit of being self-masking, a property which accommodates a long density range in the negative and yet is non-critical in exposure time. Having no colloidal binder layer, the prints on plain paper are totally matte, so the viewer experiences no reflective surface glare from the illumination. The image substance is embedded in the surface fibres of the paper sheet, which may be attractively textured, and is always sympathetic to retouching or overpainting.
The so-called pigment processes, invented by Poitevin in 1855, depend on the light-induced oxidation of organic matter by chromium(VI) in a soluble dichromate, which is itself reduced to chromium(III), a substance that causes hardening of a layer of water-soluble colloid, such as gelatin, gum acacia, casein, glue, or egg albumen, to render it locally insoluble where the light fell. Images are made visible by including a permanent pigment in the binder layer. Processes employing the light-hardening of dichromated colloids include gum bichromate, and the carbon process and its variants (e.g. Artigue, Fresson). A related group of processes employ dichromate as a bleach (or oxidant) for a silver gelatin image, replacing the silver locally with hardened gelatin, which can then selectively absorb oily printers' inks, as in the bromoil, oleobrom, carbro, ozotype, ozobrome, and oil pigment processes, where the use of a silver gelatin paper enlargement provides a very convenient starting point. The appeal of these processes lies in the extensive manipulation that is possible with the hardened colloid matrix—in the first group, the image is developed controllably by physical removal of colloid-bound pigment, in the second, by the application of oil-based ink with brush or roller.
Direct photo-decomposition of certain coloured organic substances, natural or synthetic, has been employed since the earliest days of photography. In 1839 Herschel introduced his anthotype (or phytotype) process, involving the light-bleaching of dyes (anthocyanins) extracted from crushed flower petals; although such images cannot be fixed, a few of Herschel's still survive today. The photo-decomposition of unstable diazonium compounds, together with their coupling reactions to form synthetic azo-dyes, gave rise to the diazotype, Feertype, and primuline processes, which found application in photocopying. Recently, modern photopolymers have been employed as binders for pigment images, as in Perera's Heliochrome process.
— Mike Ware
Bibliography
- Crawford, W., The Keepers of Light: A History and Working Guide to Early Photographic Processes (1979).
- Farber, R., Historic Photographic Processes (1998).
- Barnier, J., Coming into Focus (2000).
- James, C., The Book of Alternative Photographic Processes (2002).
- Rexer, L., Photography's Antiquarian Avant-Garde (2002)
