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Old 2nd February 2011, 03:34 PM
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Default Gold Toning > Chemistry Question

I've been offered some chloro-auric acid (HAuCL4.xH2O it has on the label) in a sealed vial.

I've been thinking of mixing up my own gold toner for some time but the high price of gold chloride has been just a wee bit off-putting. My chemistry knowledge (A-Level only) has deserted me somewhat after 40+ years and I'm not sure whether or not the compound in this form could be used in a toner. I've certainly not seen any formulae where it is used by that name.

I undertood chloro-auric acid to be the result of dissolving gold in aqua regia and would have expected it to be a liquid. This however is a solid, and looks remarkably like gold chloride (Au2Cl6). As you can see, it says 'gold chloride brown' on the label as well.
The fact that it is sealed in a vial to preserve it in the solid state (the chloride being extremely hygroscopic) is further suggestion that it is indeed actually gold chloride.

Any chemists here care to pass judgement/give insight?

It states that it is 51% gold, and I reckon that there is 1 gram (the contents plus vial weigh 2 grams).
Any advice as to people's opinion of the best formula to use (Nelson or otherwise?) would also be appreciated - from anyone that may have mixed gold toner themselves.

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Old 2nd February 2011, 03:47 PM
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I have a copy of an article published in Post Factory Photography No.3 called 'Making Gold Trichloride for Toning, by Liam Lawless' It was pretty controversial due to the very real dangers involved in the process. My magazines are still in boxes from our move but an internet search may help?
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Old 2nd February 2011, 04:05 PM
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Aqua regia isn't a particularly nice solution looking at wikipedia so caution could be advised . Further reading points to Chloroauric acid if thats any help?

Paul

Last edited by PMarkey; 2nd February 2011 at 04:08 PM.
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Old 2nd February 2011, 04:23 PM
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Roy, I used to mix my own gold toners at one time, and I too still have a couple of vials of gold chloride. They are usually 1gm.

My favourite gold toner formulas were;

Gold toner solution a/b:

solution A
thiourea...................4g
distilled water..........225ml

solution B
gold chloride.............1g
distilled water...........225ml

use 236ml water plus 29ml soln. A plus 29ml soln. B plus a further 236ml water, then add slowly, 5 drops of concentrated sulphuric acid. Mix well. This working solution lasts a long time and can be discarded when toning becomes too slow.

This one is a bit more user-friendly although the citric acid does not keep too well;

Gold toner 3 bath, a, b, c;

solution A
thiourea..................3.5g
distilled water.........250ml

solution B
citric acid.................3.5g
distilled water.........250ml

solution C
gold chloride............1g
distilled water..........250ml

use 1 part of each to 10 parts water.
This toner used to give the most delicate grey blue tones to chlorobromide papers like Record Rapid and was certainly a favourite of mine.

I also used to use Nelson gold toner but of course this gives brown tones, particularly effective with bromide papers.

Thiourea is nasty being carcinogenic so do not get it on your person and of course avoid breathing air-bourne dust.
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Last edited by Trevor Crone; 2nd February 2011 at 04:27 PM.
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Old 2nd February 2011, 04:23 PM
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Thanks guys for the quick responses...
@Barry: I have no intention of making my own gold chloride! Passing chlorine gas over heated gold is not something I would do willingly without a full fume hood!

@Paul: likewise to the dissolving the partner's jewellery in aqua regia route - although I do have both concentrated nitric and hydrochloric acids I've never been moved to mix them - somewhat unstable and definitely rather volatile! The chloroauric acid link is useful, seems it's just another name for gold chloride, occasionally?

@Trevor: Excellent, thanks. I seem to recall seeing similar, if not those actual, formulae. Good to know that you've used them.

Last edited by Roy_H; 2nd February 2011 at 04:27 PM.
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Old 2nd February 2011, 04:34 PM
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Roy, there is also Kodak's gold protective solution, GP-1;

distilled water..................................750ml
gold chloride, 1% stock solution......10ml
potassium thiocyanate.....................10g
water to...........................................1000m l

Use undiluted, lasts ages. Although primarily for archival purposes will give delicate blue tones on warm tone papers.
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