Practical Printing with Colloidal Gold

by Tony McLean

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.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 USA and they are, I understand, to be greatly admired. This article is based on the late American graduate chemist, photographer, and printmaker, John Rudiak’s adaptation of Dr. Ware’s scientific articles and may bear only a passing resemblance to the original “New Chrysotype” process.

Chemicals.

“The problem with trying to print (and not just tone) in gold salts prior to Mike Ware’s 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 di-sodium 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 di-sodium 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, di-sodium salt. Do not reuse. Clear for a couple minutes each in 5% EDTA, Kodak Hypo Clear, and another EDTA. Wash well. Both the paper 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, and 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.
 

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 Copyright 2001 by Tony McLean.
 All rights reserved.
 No portion of this article may be reproduced without the express permission of the author.

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