Darlington Media Group (postmaster@mediaworkshop.demon.co.uk)
Fri, 15 Oct 1999 19:11:42 +0000
Dear Gerard,
So you are interested in the Chrysotype process? I must warn you that it
can be quite dificult and expensive, and would suggest that you become
familiar with the Ziatype process to begin with as there are many
similarities. Still,if you are certain ... here is my article that was
published recently in Camera & Darkroom. It has sufficient information to
get you started.If you have any questions please do not hesitate to contact
either Lucas (who speaks several languages) or myself.
good luck! ....... Tony McLean.
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Practical printing with colloidal gold.
Gold is probably the earliest known metal to be discovered by primitive
man; probably because it is to be found in nature in the form of a pure
metal which can easily be identified and collected by techniques such as
washing or "panning" in stream beds.
Gold is a precious yellow metal. Its rarity makes it valuable as basis for
global currency. One estimate suggests that all the gold refined in the
world to date would fit within a sixty foot cube. Gold is also a relatively
unreactive metal; it does not readily form compounds with other elements
Gold also resists attack by most acids but is soluble in aqua regia, a
mixture of three parts hydrochloric acid and one part nitric acid. All gold
compounds are thermally unstable and on gentle ignition easily revert to
their metallic form.
Throughout the centuries gold has achieved an almost mystical quality. The
goal of the alchemists, who practised from 400-1400 AD, was to transmute
common elements (like lead) into gold. Because there were seven known
heavenly bodies, the alchemists believed that there were seven base
elements. Incredulously, even though in sixteenth century England, Henry IV
outlawed the alchemical production of gold, the practice continued and even
Sir Isaac Newton and two other distinguished seventeenth century
scientists, G. W. Leibniz and Robert Boyle, "the father of modern
chemistry", clearly accepted the theory of alchemical transmutation.
In 1856, M. Faraday prepared the first colloidal gold dispersion in water.
He added phosphorous to a solution of gold chloride and after a short time
noted that the blue colouration changed to a ruby red dispersion . However,
it was Sir John Herschel in 1842 who first described a method of making
photographic prints in gold. He coated a sheet of paper with a ferric
citrate and exposed the paper to the sun in contact with an etching, that
presumably had been made semi transparent. He then immersed the print in a
solution of chloroaurate (111). Unfortunately, the resulting process, which
he termed "Chrysotype," was not able to give what we would describe today,
as a continuous tone print. For a further more detailed account of the
history of this process, I must refer the readers to Dr. Mike Ware's web
site at:-
http://www.mikeware.demon.co.uk/
In the late eighties Dr.Ware, a lecturer and researcher in structural and
inorganic chemistry at the University of Manchester, set about
investigating and refining many of the old processes. After six years of
research, Dr. Ware announced to an imaging conference held in Cambridge
(U.K.) in September 1992, the first workable method of producing
photographic prints in colloidal gold. He named his discovery, with due
deference to Sir John Herschel's earlier explorations..."The New
Chrysotype."
Dr.Ware has not as yet, released the practical details of his researches
into the Chrysotype process into the public domain. He has exhibited some
of his Chrysotype images in both the U.K. and the U.S.A. and they are, I
understand, to be greatly admired. This article is based on the American
graduate chemist, photographer, and printmaker, John Rudiak's adaptation of
Dr. Wares scientific articles and may bear only a passing resemblance to
the original "New Chrysotype" process.
Chemicals.
Hydrochloroauric acid (H.AuCl4.3H2O) M.W. 393.83
Confusingly, this gold salt is also known by many other names eg.
Tetrachloroauric Acid, Trihydrate; Chloroauric Acid,Trihydrate; Hydrogen
Tetrachloroaurate, Trihydrate; Auric Chloride, Hydrochloride, Trihydrate
and just plain gold chloride, The molecular weight given above should aid
the appropriate selection from a chemical supplier. It is a yellow /
orange crystalline powder that is stable under ordinary conditions of use
and storage. but it is hygroscopic and deliquescent in moist air and
therefore it is usually supplied in sealed glass tubes. It is corrosive,
will stain the skin purple and will attack the mucous membranes. So wear a
mask and follow all necessary safety precautions whilst handling this
material.
Hydrochloroauric acid can be purchased from Johnson Mathey of Royston,
Herts., but is expensive at nearly £40 per gram. Those of you that reside
in the U.S.A. are more fortunate as this compound can be purchased from
Engelhard in New Jersey at about $7 per gram, although there is a minimum
order of $150 .
3,3 Thiodipropionic acid (C6H10O4S) M.W. 178.20
This is the compound which is at the heart of this process. It is a fine
white powder and is available in this country from Sigma Aldrich at approx
£8 for 100 g and from Lancaster chemicals, New Hampshire in the States.
Again, they seem to have a minimum order of $50. There seems to be little
safety information available on this product but normal precautions in the
handling of chemicals should be adhered to.
Quoting from The Journal of Photographic Science, Vol 42, number 5, (1994),
pp 157-161."Photographic Printing in Colloidal Gold" by Dr. Mike Ware:
"Warning: in any experimental exploration of the chemistry of this
process, it would be prudent to avoid two hazards: the precipitation of the
dangerously sensitive explosive, fulminating gold, which results when
ammonia is added to gold(III) complexes, and the possible formation of the
unpleasant vesicant, mustard gas, S(CH2CH2CL)2 by inadvertent chlorination
of the ligand."
Ammonium ferric oxalate
This is the green crystalline light sensitive compound used in both the
Ware and Ziatype versions of the "printing out "platinum palladium process.
It is available here from Silverprint in London at £3.00 for 25 g. It is
also sold by Bostick & Sullivan in the States.
The developers : E.d.t.a.-di sodium, tartaric acid, citric acid, oxalic acid.
These developers are also available from the suppliers named above. Citric
acid and tartaric acid can also be purchased locally from home wine making
shops and some chemists.
Papers.
I have limited my exploration of this process to three papers from the
Arches stable: Arches Platine, Bergger COT 320 and Arches Aquarelle. The
first two papers are starch sized and the latter, Aquarelle is sized with
gelatin. These papers are all of approximately the same weight ie 300g/m2
and have excellent wet strength. Their sizing is of a sufficient hardness
to allow the sensitiser to be spread evenly. A quick test with another
paper, Whatman H.P. (a soft sized paper) revealed that this paper was
insufficiently sized for this process and it soaked up the sensitiser like
blotting paper. Chrysotype sensitiser is far less viscous than the
traditional Pt/Pd sensitisers.
For those of you unfamiliar with the Bergger COT 320 paper, I can relate
that my first impressions are quite favourable. It is very smooth and the
colour is perhaps, a shade more neutral than that of Arches Platine. The
paper is manufactured from 100% cotton by Arches hence the similarity with
"Platine". I do not know, but I suspect that the paper is sized with
starch. It is more difficult to detect the reverse side of the COT-320 as
both sides seem equally sized and there is no watermark. However when
moistened the felt (reverse) side of this paper is immediately
recognisable. This paper is currently used by Bergger as a base for their
Prestige triple weight, silver gelatin enlarging paper and can be purchased
at a similar price to that of Platine.
Preparing the Sensitiser solutions.
I am indebted to John Rudiak of New Mexico for his interpretation of Dr.
Mike Ware's New Chrysotype process. In March of 1996, John revealed to the
"Alt. process" community, his adaptation of Dr. Ware's scientific paper,
which was previously published in the Journal of Photographic Science. vol
42 (1994). John put it into words and numbers, an account that would be
understandable to non chemists. I quote below from John Rudiak's original
E Mail:-
" The problem with trying to print (and not just tone) in gold salts prior
to Mike Wares development of the new Chrysotype process was the annoying
tendency of the gold to precipitate out of solution when a sensitiser was
mixed using the traditional photo reactive compounds, such as ferric
oxalate, etal. It seems that the "crux of the biscuit" (Zappaism- sorry)
in this process is the introduction of a suitable ligand to hang onto the
gold and keep it in solution long enough for it to be coated and dried.
Without a more complicated description of ligand chemistry, all we need to
know is that the compound is 3,3'thiodipropionic acid, (or
3,3'thiodipropanoic acid in Britain )- same stuff and that we need to use
it's disodium salt. Mike, who seems to be a fan of ammonia based systems
has chosen ferric ammonium oxalate as the light sensitive iron compound,
available here from Spectrum Chemicals. Get the ligand from Lancaster
Chemicals in NH.
The sensitiser can be compounded into three stable components which are
mixed in equal amounts just prior to coating the paper.
Part A of the sensitiser is the gold component and is made by taking a 0.9M
solution (35.4%) of gold chloride and adding to it slowly and equal amount
of 0.9M sodium hydroxide (3.6%)
Part B is the ligand, and is in a 1.25M strength. We want the disodium
salt, so take 100ml. water (all distilled here) and add 9.0 gm. sodium
hydroxide, COOL, and then add 20.0 gm, TDPA.
Part C is the ammonium ferric oxalate, in a 0.45M conc., which works out to
19.3 gm in 100ml water.
These will hold up very well if kept separate, the FAO being the least
stable.The exposure is very similar in duration and wavelength requirements
to Pt/Pd.
After exposure, develop in a 1% soln of either tartaric, citric, or oxalic
acid, or even EDTA, disodium salt. Do not reuse. Clear for a couple minutes
each in 5% EDTA, Kodak Hypo Clear, and another EDTA. Wash well. Paper
choice and developer choice influence final colour of the print- haven't
had time to try out all parameters.
The process is very sensitive to humidity of the coated paper, changing the
colour of the prints due to the differing sizes of the deposited colloidal
gold particles. I have prints showing a split, with blue highlights and
burgundy shadows."
---------------------------------------------------------
I have taken the liberty of simplifying John's instructions even further to
give the reader more manageable quantities of the three constituents
suitable for an exploration of the Chrysotype process. Note:- All water to
be distilled.
If you are of a nervous disposition, or do not possess the necessary skills
or equipment to make up these solutions, then I would advise you to make
contact with the chemistry department of your local college. The promise of
an original print will usually be enough to persuade a technician to
prepare this chemistry for you.
PART A
For gold chloride supplied by Johnson Mathey in 1g glass tubes:- add 3 ml
of distilled water with a new 1 ml syringe directly to the opened tube. The
gold compound should dissolve immediately. Transfer this gold solution to a
clean 10 ml brown dropper bottle with the syringe. Add the remaining 0.5
ml of water to the tube, replace the cap, shake gently then transfer the
remnants to the dropper bottle. Now weigh 1.8 g of sodium hydroxide (the
beads are easier to handle than the NaOH crystals) and transfer this to a
clean 50 ml graduate containing 30 ml of water, swirl to dissolve and top
up to 50 ml with water. Add 3.5 ml of this sodium hydroxide solution to the
dropper bottle containing the gold with a syringe slowly, to aid the
dispersion of heat, at no more than 0.5 ml increments. Replace the cap,
label and discard the remaining sodium hydroxide solution. This should
provide you with approx 7.0 ml of sodium tetrachloroaurate (18%) - enough
to make 70 number 5 x 4 prints.
PART B
As per J.R.'s instructions but divide the quantities by five to make up 20
ml of the ligand and transfer to a suitably labelled 20 ml dropper bottle.
This solution may be unstable so make up only enough to satisfy your needs
for a month.
PART C
Again, as per John's instructions. Under tungsten light, dissolve 2g of
a.f.o. in 8 ml of water and top up to 10 ml. Transfer to a clean brown 10
ml dropper bottle.
Method
All utensils must be kept clean. More so than with any other alternative
process, cross contamination must be avoided. Use new trays and syringes
and wash everything immediately after coating each sheet of paper. The
mixed sensitiser will keep for only half an hour or so, then it will reduce
out as metallic gold. Anyone wish to buy a gold plated syringe?
All steps to be carried out under low level tungsten light
For a 5x4 print:
Take 4 drops of the ligand (T.D.P.A.) and add to it 2 drops of the gold
solution. It should now be apparent that the yellow colour of the gold
solution has been "neutralised" by the ligand and that the solution is now
clear.
Actually, the ligand converts the gold from its trivalent state (Au+++) to
its monovalent (Au+) state. Monovalent gold chloride requires far less
energy to reduce to its metallic gold state than the trivalent gold. Now
add 2 drops of ferric ammonium oxalate (f.a.o.) The sensitiser should now
be a pale green colour.
With some papers, notably Arches Aquarelle, one drop of a 2% solution of
Tween 20 added after the gold can improve the smoothness of the print and
prevent image bleed in the developer, especially at low humidities 50-75%
R.H., when much of the image develops out.
Spread the sensitiser over the paper using a glass rod. Two or three passes
should be adequate. Dry the paper using the cool setting on a hair drier
and hang the paper in a dark place at the humidity you require. (see note
on humidity and image colours)
Place your negative in contact with the emulsion and place in a printing
frame. The speed of the sensitiser is about twice that of a normal lithium
Ziatype without any contrast (dichromate) additive. Expose to a source of
ultra violet radiation ie. sun lamp. At relatively high humidities the
image will totally print out and can be inspected and removed when judged
complete. At lower humidities there is only a partial print out of the
shadow and mid-tones, so test strips may be necessary but these must be
maintained at the same humidity as the final print.
The exposed print is quickly and smoothly immersed in the developer at
approx 20 C and the tray rocked continuously. Developer concentration
should not exceed one per cent and you should err on the side of a little
less rather than a little more. Again, at high R.H. little or no
development will happen. However with less humidity and partial print-out,
the image will quickly appear on immersion and gain density over a period
of thirty seconds.The colours may change from blue through to purple over
a period of one to two minutes. With luck, it may be possible to achieve a
good split with purple shadows and pale blue highlights Remove the print
from the developer and place it in a water bath for a couple of minutes,
This will curtail any further development. Throw the used developer
away...remember it is one shot and cannot be reused. After several printing
sessions you will notice that your brand new developing tray will be plated
blue with colloidal gold. Just remove as much as you are able with a damp
towel at the end of each session.
Clear the prints in two or three baths of whatever clearing agent you have
at hand. Either E.D.T.A. di-sodium, hypo-clear, or "Lime-Away" at the
usual percentage dilutions necessary in Pd/Pt printing. Wash for 30
minutes or so and hang to dry.
Printing Problems.
During my investigation of this process there have been times when I have
been plagued by print defects. Often a particle or two of gold will
precipitate out during the coating of the paper and will leave a meteorite
trail down the print parallel with the direction of the glass rod.
Obviously these trails will be more apparent in areas of continuous tone
such a skies. If they are small they can often be carefully abraded away in
the wash water using a fingertip. Small spots can similarly be etched away
with a knife blade.
John Rudiak's instructions require that the sensitiser be made up from
equal proportions of the T.D.P.A. (ligand), gold and f.a.o. Theoretically
this may be so, but I have found that it is often necessary to increase
the proportion of the ligand in order to prevent precipitation of the
colloidal gold prior to exposure, hence my use of four drops of the ligand
in my instructions for a 5 x 4 print. Also, the number of reject prints
spoiled by pre-exposure precipitation seems to diminish over a period of a
few weeks which has led me to believe that the ligand improves with age. Of
course, numerous manufacturers will sell you variations H.AuCl4 3H2O with
differing gold contents. The best quality should have a gold content of
around 50% but variations may require recalculation of the concentration of
the ligand.
If your print includes a border of sensitiser, like mine, this will often
bleed into the surrounding picture area, especially at low R.H.'s when much
of the image appears during development. With some papers, the addition of
1 drop of 2% Tween seems to lessen the effect of of image bleed. However,
Tween does not appear to be compatible with either Arches Platine or
Bergger COT 320. If you find that this bleed intrusive, then it is a simple
matter to mask your borders with a ruby lith film, but with the loss of
those "arty" borders.
Humidity and colour control.
Without going to the trouble of constructing bespoke humidity chambers
containing saturated solutions of various chemicals necessary to maintain a
constant humidity, it is indeed difficult to control and maintain a
specific R.H. However, an inexpensive hygrometer will give a good
indication of the ambient humidity in the room where your sensitised paper
is left prior to exposure. The simplest method is to maintain a room or
enclosure at a relatively high R.H. say 80% and to introduce the dried
sensitised paper to this atmosphere for a measured period of time. For
example, a print dried with a cool stream of air will still have a moisture
content of about 50%. Left for 5 minutes the paper will have absorbed
moisture from the surrounding air and have a R.H. of approx. 70% and full
ambient humidity of 80% will be achieved after 15-20 minutes. I know this
is rough and ready but it seems to work for me.
The size of the colloidal gold particles will determine the colour of the
final print. Humidity has the greatest influence of all on the size of the
reduced gold, with length of time of immersion in the developer, the
choice, concentration and temperature of the developer being of notable but
of secondary importance.
At a high R.H. of 80% and above, there will be full print out and a blue /
black image. At a R.H. of approx 65 - 70% the print will have maroon
shadows, blue mid tones and grey / blue highlights. At a R.H. of 60% and
below there will be only partial print out and the print will be largely
maroon with pale grey highlights.
The four step wedges in the illustration will give an indication of the
colours to expect at differing humidities, together with the dynamic range
of the process; which is about 14 steps of 0.15 density units ie. approx 7
stops.
I have experimented with three developers.....oxalic, citric, and tartaric
acids. There seems not a great deal to choose between them as far as
controlling the colour of the final image. Of the three, I would suggest
that oxalic acid, at a dilution of 0.8%, is most efficacious.
Contrast control
As with the traditional and contemporary Pt/Pd processes, there is no
substitute for an original long scale negative. Thin negatives will print
with amazing speed and with insufficient time for proper control. Negatives
developed in a pyro developer (P.M.K.) print very well indeed. If a little
contrast boost is found to be necessary, one drop of 3% hydrogen peroxide
added to the sensitiser will increase the contrast of the print. Any
further addition will lead to print granularity.
Summary.
This is indeed an intriguing process but not one for the feint of heart. I
have managed to make, over the course of several months, some of the most
exquisite prints of my "alternative" career. Colours and split tones can
range from the subtle to the surreal. I have had neither the time nor the
finances to make a full exploration of this process but will certainly
return to this technique in the near future. One benefit of this research
is that I now see the world in reds and blues instead of just plain
monochrome and I find myself continually looking for photographic
opportunities in which to exploit the new palette of colours provided by
this process.
One aspect of this process that I haven't mentioned is that of permanence.
Elemental gold is as permanent as platinum or palladium. Prints made with
Pt/Pd family metals have been with us for over a century. I suspect that
colloidal gold may be even more archival than that of Pt or Pd. Although
these elements are relatively inert, they do act as catalysts for several
chemical reactions which could, in certain special circumstances, lead to
breakdown of the paper fibres. The colloidal particles of gold, unlike the
dyes of the colour print, will not fade with time. The beauty and rarity of
a carefully made print in colloidal gold will be as permanent as poetry.
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