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Sequence viewing > Index - Alternative Photo Emulsions - Resource - ©
Lloyd Godman
Alternative
Photographic Processes - (Hand
made photographic -emulsions and processes)
Processes
- The Argyrotype
Introduction:
Within the whole gamut of iron-based processes, printing in platinum,
palladium or gold stands supreme for quality and permanence, but the
expense of these options deters many practitioners from attempting them.
At the other end of the iron-alternative scale is the cyanotype process,
providing an image in Prussian Blue: it's truly inexpensive but limited
by a colour that is rather strident for some tastes and subject matter.
In the centre stand the iron-based silver printing processes, which
can aspire to the qualities of platinum without its expense - but also
without its certain permanence. Iron-silver processes are useful as
an introduction to alternative printing for teaching workshops, for
proofing large format negatives, and as a starting point for further
toning of the colloidal silver image. It may seem perverse to make silver
images on plain paper indirectly, via the photochemistry of iron(III)
carboxylates, when they can be made directly by means of the salted-paper
process using silver chloride, but the latter is not as simple and straightforward
as it is sometimes represented, if a reasonably enduring result is desired.
History Sir John Herschel, who made so many contributions to photography,
was the first to devise an iron-silver process, which he dubbed Argentotype
in 1842. Since then there have been many derivatives of his invention:
Van Dyke, Kallitype, Sepiaprint, and Brownprint are names known to most
of us. Some of these recipes have achieved - for no evident reasons
- an almost Byzantine complexity; others are said to be 'deficient in
gradation', and most have acquired a rather poor reputation for image
stability and permanence. In 'The Complete Photographer' of 1932, R.
Child Bayley described his experiences thus: "...a batch of kallitype
prints turned out of a drawer the other day bore no sign to distinguish
the front of the paper from the back. The image which once had been
vigorous enough, had folded its tents like the Arab and had silently
stolen away." In skilled hands, however, there is no doubt that
these processes are capable of fine results, and there is no better
contemporary source on their practice than Dick Stevens' comprehensive
study 'Making Kallitypes - a Definitive Guide', to which I would commend
every interested reader. Even Dick Stevens would admit, though, that
none of these processes is free from pitfalls or difficulties. In the
interests of achieving a more 'user-friendly' plain paper silver process,
I re-visited the underlying chemistry in 1990, and came up with an easier
(I don't say "better") process, which I called Argyrotype.
This article outlines my chemical reasoning, and describes the details
of preparing and processing the sensitized paper. Structure and Stability
of Silver Images Brown silver images consist of metal particles much
smaller than those constituting the black silver images of modern gelatine-silver
halide papers; the former have colloidal dimensions (ca. 20nm) - far
smaller than the wavelengths of visible light (ca. 500nm) - and their
colour is due to a specific absorption of light which is dependent on
their shape, size, state of aggregation and chemical environment. Such
small particles are inevitably more vulnerable to chemical attack: they
present a relatively large surface area and are rapidly dissolved by
reagents that 'etch' or 'bleach' (i.e. oxidise) silver. The inherent
problem of the iron-based silver processes lies in the danger of leaving
residual ferric iron in the print - to its ultimate undoing, because
iron(III) will oxidise silver with consequent degradation of the image.
It is this problem that the Argyrotype process has been designed to
avert. An Alternative Silver Salt Without exception all the iron-silver
processes to date have used the most commonly available soluble salt
of the metal, namely silver nitrate. But nitrate is an oxidising anion,
and tends to dissolve the colloidal image silver during wet processing,
especially under acidic conditions. To minimise this loss of image the
Kallitype process employs alkaline-buffered developers of high pH, e.g.
Borax. Alas, these create a new problem, because they cause hydrolysis
of the excess iron(III) in the sensitizer and the deposition of insoluble
ferric hydroxide in the image, which ultimately causes it to fade. In
principle the cure is simple: replace silver nitrate with a soluble
salt of silver having a non-oxidising anion. There are a few such salts
known to chemistry, but most of them, e.g. silver fluoride, have unacceptable
properties or a level of toxicity that debar them from 'home chemistry'.
There is, however, a little-known and relatively innocuous silver salt
that does fit the bill: Silver Sulphamate, NH2SO3Ag. This cannot be
bought, but is easily made in situ, as I describe below. It can be employed
in an acidic sensitizer of pH 2 to 3, which will wash out of the paper
cleanly, without hydrolysis of the excess ferric iron, and without any
tendency to dissolve the colloidal silver image. Chemicals needed for
the Sensitizer Sulphamic acid (spelt 'sulfamic' in the USA) NH2SO3H
.....7 g Silver(I) Oxide Ag2O ............................................................7
g Ammonium Iron(III) Citrate (the green form) ....................22
g Tween 20 (wetting agent; amount variable) ........................0.2
cc Distilled water to make ......................................................100
cc GPR (98%) grade of purity is adequate in all cases. Making up the
Sensitizer (under tungsten lighting only) Heat 70 cc distilled water
to 50-60 °C, and dissolve 7 g Sulphamic Acid in it. Add 7 g powdered
Silver(I) Oxide to the hot solution (1) in small amounts with vigorous
stirring until all is dissolved. Add 22 g Ammonium Iron(III) Citrate
(the green variety) in portions to the warm solution (2), stirring until
it is all dissolved. Allow to cool. Add 0.2 cc Tween 20 and mix well.
(The optimum quantity of this wetting agent will depend on the paper
used.) Add distilled water (at room temperature) to make a final volume
of 100 cc and filter the solution to remove any small amount of solid
remaining. (The solution should be a clear deep olive-green colour.)
Store in a brown bottle in the dark at room temperature. (The solution
should keep for a year, at least. If it throws down a small amount of
black precipitate, it should be re-filtered.) To make a more contrasty
sensitizer, dissolve an extra 1 g Sulphamic Acid in 100 cc sensitizer.
Some Alternatives in the Chemistry If Silver(I) Oxide is difficult to
obtain, 8.4 g Silver Carbonate may be used instead; but it should be
dissolved at room temperature in a tall vessel - a 250 or 500 cc measuring
cylinder to contain the spray; adding the Silver Carbonate in small
portions, and allowing the effervescence to die down each time. Alternatively,
7 g Silver(I) Oxide may be precipitated from a solution of 10.3 g Silver
Nitrate by adding a solution of 2.5 g Sodium Hydroxide; after filtration
and washing, the moist precipitate may be dissolved in the Sulphamic
Acid. If you prefer to avoid the difficulties of obtaining and manipulating
the chemicals, then ready made-up Argyrotype sensitizer solution can
be purchased from Vintage Image, Fotospeed, Silverprint or Luminos.
Choice of Paper The purity of the paper is crucial to the success of
this process. Only the best cotton fibre, internally sized with Aquapel
and free of other additives, will do. Papers that I have found to work
well are Whatman's Watercolour or Printmaking papers and Atlantis Silversafe
Photostore - also made by Whatman - (preferably in the 200 gsm weight);
but the best (of course!) is Ruscombe Mill's handmade Buxton paper.
The non-ionic surfactant, Tween 20, is included in the sensitizer formulation
to assist uptake of the sensitizer by the cellulose fibres, which minimises
"bleeding" of the colloidal metal image during processing,
but it may cause uneven penetration of some papers that contain a mixture
of fibres. There is always room for experiment with other papers, but
you may find that those which do not meet this specification will stain
or lose image substance. Coating The sensitizer solution can be brushed
onto the paper, but this is wasteful, expensive and uneven. It is more
economical to coat by means of a glass rod, as I have described in detail
elsewhere. About 1.6 cc will be needed to coat a 10"x8". Allow
a few minutes for the sensitizer to soak in, until the paper surface
appears non-reflective, then dry for about 10 minutes in a stream of
warm (40 °C) air. Alternatively, simply allow it to dry at room
temperature and humidity for about an hour. The sensitized paper should
be used within a few hours, unless a desiccated box is available for
longer term storage: shelf life in a dry environment is at least a week.
Printing As with platinum-palladium printing, a negative having a long
density range (ca. 0.2 to 2, or so) is desirable, obtained by overdeveloping
by about 70%. Softer negatives may be accommodated by using the more
contrasty sensitizer recipe. [Indeed, by mixing the two formulations,
the contrast of the sensitizer could be fine-tuned.] As with most other
alternative processes, the sensitizer is very slow, so printing must
be by contact with a large format negative, using an ultra-violet lamp
or sunlight, for which the exposure will be comparable with other iron-based
processes. If the humidity of the paper is normal (under an ambient
RH between 40% and 80%), a detailed print-out image will be obtained,
orange-brown on a yellow background, which gives a good indication of
the correct exposure, making test strips unnecessary. A little development
(half to one stop) can subsequently be expected to occur in the high
values during wet processing, and there will be considerable 'dry-down'
of the tonality. Both these factors should be taken into account in
judging exposure; the colour will also darken to a rich brown in the
fixer bath. It is better to overexpose than underexpose, because a dense
image can always be reduced. Adjustment of Colour The colour of the
print-out image may be shifted to a more neutral tone - an attractive
purplish-grey - if the sensitized paper is humidified before exposure
by leaving it above water (100% RH) for 30 minutes at room temperature.
This is a very economical method of colour control! A word of caution
though: humidified sensitized paper can damage negatives during contact
printing unless a protective layer of very thin polyester film is interposed
between the two, and this may worsen the sharpness of the image. Wet
Processing Processing is extremely simple and non-critical, requiring
only one inexpensive solution, 2% Sodium Thiosulphate, prepared by dissolving
about 20 g of the crystals in 1 litre of water. This bath has a capacity
of about ten 10"x8" prints and should be replaced when necessary.
Wash the print for 5 minutes in water at room temperature - either running
or replaced two or three times (avoid using highly chlorinated water
which will damage the silver image). The yellow unexposed sensitizer
of excess iron and silver salts should be completely washed out within
this time. If there is any 'bleeding' of colloidal silver metal, indicated
by a red-brown stain running off dense areas of the image, then the
paper fibres are failing to trap the colloidal silver particles, and
it is likely that insufficient Tween has been used or the paper is unsuitable.
The effects of 'bleeding' may be minimised by processing the print face
down, to avoid staining adjacent areas, but there will be some density
loss. If a particularly long tonal range is desired with very delicate
high value gradations, the exposed print should be left in a humid atmosphere
(100% RH) for ten minutes before wet processing; several steps of highlight
detail will build up. Alternatively, you can just breath heavily on
it! (The Huurrrotype?) Fix the print in 2% Sodium Thiosulphate solution
for 3 minutes. This removes any traces of insoluble silver salts and
intensifies the image: the shadow gradation strengthens, and the colour
rapidly shifts from red to brown. Overlong treatment in this bath and
exposure to air can result in loss of image density especially in the
highlights; this may be used to reduce an overexposed print, or a standard,
non-acid fixer may be used. If, on the other hand, very delicate highlight
detail is desired, a little ammonia may be added to the clearing bath
to make it distinctly alkaline (pH 9 to 10); this inhibits the dissolution
of silver, but may raise the level of residual iron in the image. Wash
the print in water for 20 minutes and air dry at room temperature. The
image 'dries down' significantly - at least one Zone. Heat drying on
a ferrotype plate, or by ironing, may shift the colour to a more neutral
blackish brown. Unlike silver-gelatine papers, there is no tendency
for plain paper prints to curl, and their surfaces are never tacky.
Retouching is easily performed on the receptive paper surface with best
quality watercolour paints. Image Permanence Like any colloidal silver
image, especially those on plain paper unprotected by a colloid binder
layer, an Argyrotype is inevitably rather susceptible to attack by oxidising
acids and sulphur-containing substances. However the residual iron and
silver in the unexposed areas should be very low and image stability
and lightfastness are good. If improved permanence is desired, the image
is receptive to the usual toning agents (e.g. selenium or gold), though
these may have to be used at a lower concentration than usual. Not having
tested them all, I should be glad to hear of people's experience with
such toners. Precautions and Disclaimer The sensitizer solution is irritant
and toxic, and will stain skin and fabrics: wash away any spillages
with plenty of cold water. However, it is believed that the rest of
this process incurs very little risk. An ultra-violet lamp must of course
be shielded from accidental viewing. References Dick Stevens, 'Making
Kallitypes - A Definitive Guide', Focal Press, Boston, 1993. William
Crawford, 'The Keepers of Light', Morgan and Morgan, New York, 1979.
Jaromir Kosar, 'Light Sensitive Systems: Chemistry and Application of
Non Silver Halide Photographic Processes', John Wiley and Sons, New
York, 1965. Mike Ware, 'Mechanisms of Image Deterioration in Early Photographs
- the sensitivity to light of WHF Talbot's halide-fixed images 1834-1844',
Science Museum and National Museum of Photography, Film & Television,
1994. First published in the British Journal of Photography, Vol. 139,
No. 6824, 13 June 1991, pp. 17-19.
http://www.edinphoto.org.uk/1/1_early_photography_-_processes.htm
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