Paper for Alternative Printing
Background to the ProblemAlternative photographic printing involves the hand-coating of plain paper with solutions of light-sensitive chemicals. There is an important sub-group of alternative processes which have one feature in common: they are all based on light-sensitive salts of iron. Many readers will already be acquainted with some of these, for instance, the Platinotype, Palladiotype, Chrysotype, Argyrotype and Cyanotype processes, in which the final image consists, respectively, of platinum, palladium, gold, silver or Prussian blue. In all these processes (and their relatives, such as the Kallitype, Vandyke, Argentotype, Amphitype, and Sepiaprint), a solution of reactive chemicals is absorbed by the surface fibres of a fine paper, where the photochemistry takes place in intimate contact with all the substances that are contained in the paper. This distinguishes the iron-based processes from conventional silver-gelatin printing and those alterantive processes using pigmented colloids, such as Gum Dichromate, or Carbon printing, where the photochemistry is isolated within a binder layer of polymer lying on top of the paper substrate.
Workers with the iron-based processes, like myself, are perpetually confronted with the difficulty of finding a paper that satisfies all four of the following criteria:
- It must be chemically compatible with the sensitizer.
- It must have sufficient wet strength to withstand processing.
- It should fulfill the requirements for archival permanence.
- It must provide an aesthetically satisfying image surface.
Machine-made papersPaper is produced commercially by machines in such large volume that it is uneconomic for the manufacturer to conduct experiments with small makings in order to perfect a specification for the minority user. Moreover, the large scale mills of the papermaking industry tend to be reluctant to disclose details of their furnishes and the additives to the pulp, so the lack of any dialogue on these matters leads to the inclusion of substances that interfere with the chemistry of alternative processes. Even worse, paper manufacturers have been known to change their specifications without notice, which may completely alter the chemical characteristics of the paper (the Palladio Company in the USA experienced just such a problem in 1989, for example).
A compromise solution that I have recommended in the past is the use of Atlantis Silversafe Photostore. This was actually developed for use by conservators as a wrapping paper for photographic archives. It fulfils very high, published standards of chemical purity and is consequently an excellent substrate for experimental work but, being a wrapping paper, it naturally lacks the aesthetic qualities desirable in a fine print, moreover its absorbency tends to be rather high for aqueous coatings and its wet strength is rather low.
Very recently, the famous Arches Mill in France has marketed a paper - Arches Platine - which, as its name implies, is specifically intended for platinum printing. This was commissioned in response to demand from the USA: early opinion there (as voiced in the Alternative Photo Process list on the Internet) reflects a qualified approval. I have found it to work well enough with platinum-palladium, but it is reluctant to yield a good result in pure platinum with the print-out process. (It may be better suited to the traditional method, which is still used by many platinum-palladium printers in North America.) Arches Platine also provides a fair cyanotype paper, but it is not suitable for my Argyrotype process. Cranes Platinotype paper is also available to North American users, and I am told that it answers well for this pupose.
The Solution: Handmade PaperThe only complete answer to these problems, which enables us to gain some control over the paper specification, is to commission a special paper to be made by hand. Fortunately there still remain in this country (UK) a few craftspeople who have kept alive the skills of hand-making paper, and it is only through the willing and patient cooperation of one of these craftsmen, that the present initiative has been possible.
The making of a paper for iron-based alternative processes was developed by Chris Bingham of Ruscombe Mill in Gloucestershire, in response to initial specifications that I drew up in 1992. The name that Chris chose for it was Buxton paper - a nice reference to my home town, noted for its spa waters! The evolution of Buxton paper has called for several painstaking trial makings by Chris, my testing the product each time by alternative photographic printing, and then much frank discussion and negotiation between the two of us in solving the problems.
The specification of Buxton paper has been carefully worked out with the iron-based processes particularly in mind, but I hope it may be useful for other processes also: Judy Seigel has found that it performs very well indeed with single-coat gum-bichromate, and it also responds very well in ink-jet printers! The composition is compatible with the chemistry that will take place within its fibres, and it is also intended to offer the highest standards of image quality and archival permanence, provided the correct wet processing procedures are followed.
The SpecificationIn summary, the specification of Buxton paper is as follows:
- It is made from long cotton fibre, nearly 100% alpha-cellulose
- The papermaking mold is wove (not laid), with no watermark
- It is internally sized with alkyl ketene dimer, 'Aquapel'
- There is no added buffer of chalk to provide the 'alkaline reserve' so popular in archival papers: calcium carbonate reacts unfavourably with iron-based sensitizer solutions
- The paper has a natural white colour, with no added pigments
- There are no other additives whatsoever, such as the optical brightening agents, bleaches, buffers, dyes, clay fillers, wet strength agents, etc., which are so commonly encountered in commercial papers, and which are most often inimical to iron-based photochemistry
- The pH is approximately 7.5, very close to neutrality
- A relatively light weight of 160 gsm has been chosen for the sheet, in the interests of efficient washing out of the excess sensitizer chemicals, and yet providing sufficient wet strength to withstand considerable handling in the wet processing.
- The paper has been cold-pressed, leaving an attractive 'tooth' to give life to the surface, which does not change significantly after wet processing. In contrast, many of the highly calendered, hot-pressed commercial papers lose some of their smoothness on wet processing.
- Being hand-made, Buxton paper has no preferred 'machine direction', i.e. the fibres are randomly oriented. It is therefore equally strong in all directions and dries flat without cockling or curling.
- The dimensional stability is high: its size changes by less than 0.5% after a cycle of wet processing and drying, making it suitable for multiple printing, where accurate re-registration of the image is paramount. The attractive texture of the surface may also commend it as a substrate for gum dichromate, and the other alternative printing processes employing a layer of photohardened colloid.
The Importance of Correct AbsorbencyThe degree of internal sizing has been chosen so that this paper is initially somewhat hydrophobic, i.e. slightly water repellant. This is intended to allow time for an aqueous sensitizer to be uniformly spread over the surface of the sheet before it starts absorbing into the fibres. It is undesirable that a sensitizer should soak rapidly into the interior of the sheet, where it cannot contribute to the image and may resist washing out.
Workers with the iron-based processes must recognise that the absorbency of a paper varies with the sensitizer solution being applied to it. The viscosity, surface tension and chemical composition (which influences its ability to swell cellulose) are all important factors. Sensitizers employing ammonium iron(III) citrate (Argyrotype, Vandyke , Brownprint and traditional Cyanotype) cannot easily penetrate the cellulose structure; the sensitizer just tends to lie on the surface of the paper or in the open pores between the fibres, rather than diffusing into the capillaries of its intrafibrillar space. Two problems may result:
- when the coating dries, crystals may be formed on the surface, which will leave marks on the image and may damage the photographic negative on contact printing
- the image substance will tend to wash out during the wet processing, because its tiny particles (often of colloidal dimensions) are not physically trapped within the cellulose capillaries; the result will be a weak picture and wasted sensitizer.
To overcome these problems, a wetting agent may be added to the sensitizer. I favour the non-ionic surfactant, Tween 20, (polyoxyethylenesorbitan monolaurate) at a concentration of about 0.2% to 0.5%, depending on the paper, which seems compatible with all the usual sensitizer chemicals.
In contrast, sensitizer solutions based on ammonium iron(III) oxalate (my processes for Platinum, Palladium, Chrysotype and New Cyanotype) appear to penetrate cellulose fibres quite readily: they suffer less from these two problems, and require very little additional wetting agent (0.1% at most, helps to reduce the contact angle and facilitates rod-coating). If the sensitizer is allowed to diffuse too deeply within the paper, the image will seem flat and 'sunken'. The control of the paper absorbency towards the sensitizer is certainly the key to quality in hand-coated print-making.
Use and PerformanceBuxton paper is currently available in Imperial sheet size (22x30 inches or 56x76 cm) with four deckle edges, of course. Because it is hand-made, users should not expect the sheet to have quite the uniformity as a machine-made product. Its individuality should be a source of pleasure to the maker of handcrafted prints; it is not intended as a beginners' paper. If you find that coating by the glass rod method proves difficult, due to slight variations in the thickness of a sheet and the 'hard' sizing of the surface, I recommended that you use a resilient sheet of foam rubber, rather than a glass plate, as the support and syringe out two strips of sensitizer solution - one at the top and one at the bottom of the area to be coated. Even if the line of sensitizer 'beads up' as it is drawn down the paper, when the unbroken strip at the bottom is picked up by the rod, it usually suffices to fill in the gaps, if a firm pressure is applied. Coating may also go more smoothly if the sheet is pre-humidified. Brush coating, on the other hand, should present no problems.
The reward for all this trouble (and expense!) lies in the sheer quality of the images obtainable on Buxton paper: experimental comparisons with popular machine-made papers, by exposure of a Kodak step tablet under controlled conditions, find that Buxton paper provides a superior tonal range and separation, image colour and maximum density in all the processes I have named: Platinotype, Palladiotype, Chrysotype, Argyrotype and Cyanotype. (The only commercial paper I have ever found that works acceptably with all of these processes is Atlantis Silversafe). In particular, Buxton paper can yield superb images in pure platinum - which are not to be confused with the so-called 'platinum' prints commonly made from a mixture of platinum and palladium - consisting mostly of the latter. Platinotype by the humid print-out method is a most exacting test of paper quality, because many impurities interfere with it. This is one reason why many 'platinum' printers today have come to use a platinum/palladium mix. They need do so no longer.
Buxton paper can be ordered from:
Ruscombe Paper Mill
4 Cours Pey-Berland
tel +33 (0)5 5788 7377
fax +33 (0)5 5788 7392
First published in Ag+ Photographic No.7 (1995).
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