View Full Version : Gold sensitization of photographic emulsion

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11-20-2011, 04:00 AM
In 2007 there was a very active thread here called "How was Technical Pan emulsion different?". There was plenty of fascinating insights and a general consensus that gold sensitization was part of the Tech pan story. Some commentators said Gold sensitization was the only new technology to come of of the WWII German reparations programme. I have been working for the better part of last week in the Imperial War Museum archives trying to prove this point. But what I cannot find in the published BIOS/CIOS/FIAT reports is anything about gold. The only lead is a mention of "Patent application relating to Sensitizing photographic silver halide emulsion" with the PB number 51575. Anyone familiar with this?

Koslowski said to be the father of gold sensitization is there in the intelligence record (as Korlowski) along with Dr Meuller but the record card states their papers concern Viscose production, problems of corrosion, Dyeing, viscose spinning and 'photographic emulsions' - these were microfilmed as PB70053 frames 1-971. Neither of these PB number become published reports - i.e. they don't appear in the index of the Classified List of Office of technical Services Printed Reports.

I have read:
Berg, W.F. (1979) Gold sensitization in photography. Gold Bulletin, 12, 97-98.
Ellis, P. (1975) Gold in Photography. Gold Bulletin, 8, 7-12.
Mueller, F.W.H. (1949) Some remarks on gold treatment of photographic silver halide emulsions. JOSA, 39, 494-496.

Mike Ware's take: "a number of researchers found that an even greater sensitising effect could be produced in silver halide gelatin by the addition of trace amounts of gold salts to the emulsion, but this was accompanied by a disadvantageous increase in fog. It was not until 1936 that Koslowsky, working for Agfa, found that the use of Gold (I) as dithiocyanatoaureate (I), the same substance that is formed in the gold toner mentioned above, could increase the emulsion speed while avoiding the problem of fogging. Gold sensitivity of silver-gelatin emulsions was kept secret for several years before any information was published, and the topic continues to be subject to close commercial confidentiality. The sensitization is thought to involve replacement of some of the silver atoms in the latent image with gold atoms, which are more readily reducible by the developer, but the mechanism is still a problem at the frontiers of photochemical research, which takes it beyond the scope of this book." He quotes Berg and Ellis.

Can anyone point me at a published source - or even a unpublished source! - that specifically concerns Koslowski's gold sensitization.

Sorry this post is of historic rather than practical significance but there seems to be no other forum to discuss such topics.

David Prakel

11-20-2011, 11:24 AM
Tech Pan- The best product ever made and droped by Kodak.

11-26-2011, 07:33 AM
Hi David,

Interesting research you're doing. I hope you've had luck getting additional info since you posted this, but in case not, I have a few bits.

Tadaaki Tani, in his book, Photographic Sensitivity, Oxford University Press, 1995, Section 6.3 on p 176, 'Gold Sensitization and Gold Latensification', states, "In collaboration with Mueller in 1936, Koslowsky discovered gold sensitization by the use of chloroauric acid and thiocyanate." Tani references R.Koslowsky, Z. Wiss. Photogr.,46, 65(1951), and F.W.H. Mueller, Photogr. Sci. Eng., 10,338(1966), along with the J.Opt.Soc.Am article you read.

Steigmann also did a lot of work with gold sensitization. Chasing down his publications (and he wrote a lot) might give you more info. I favor one of his gold brews in my negative emulsions.

The British Journal of Photography, 1945, p 333, describes Patent No. 570,393, of February 13, 1942, by Cecil Walker, Ronald Bernard Collins and Edward Cyril Dodd, all of 23, Roden Street, Ilford, Essex: "Gold Salts in Light-Sensitive Emulsions". I have that journal volume in my library, and I can copy p.333 if you don't have access to it.


Photo Engineer
11-26-2011, 10:05 AM
The Kodak records that I am familiar with give no dates, but merely show that Sheppard began the use of Sulfur as allyl thiourea to sensitize emulsions chemically. Later reports show use of Thiosulfate and then Thiosulfate with Gold. Agfa records show Thiocyanate as being used and then Thiocyanate + Gold. Both companies used a S + Au sensitization from before mid century, but it is unclear when the practice started as it is shrouded in "secrecy". One thing is clear and that is that both companies used these but with different compounds in play in the actual chemical reaction.

The use is usually 1 part of Gold to 3 parts of Sulfur. If you use Thiosulfate, then Thiocyanate can be added to accelerate the reaction or intensity the reaction. TAI (Tetra Aza Indene) can be used to restrain fog, but there are many publications listing alternate chemicals that inhibit excess fog growth.

Now, the above applies to AgBrI emulsions. It was not until the mid to late 70s that S+Au was applied to AgCl or AgClBr emulsions due to the excessive fog growth and lowering of contrast.


11-26-2011, 10:44 AM
If we're moving deeper and further back into the history of gold sensitization (and chemical sensitization, in general) Yes! let's :) -- among the earliest reference is by Carroll and Hubbard in their 1928 research paper "Sensitization of Photographic Emulsions by Colloidal Materials", later bound together with other related papers in The Photographic Emulsion, readable here: http://www.thelightfarm.com/Map/LiteratureList/LiteratureListPart1.htm (second pictured title). P 46 starts a section called "Sensitization with Colloidal Gold." The research was in its infancy, and Sheppard almost certainly played a role, but primarily through his seminal discoveries involving sensitization spots on AgX crystal flaws.

11-26-2011, 11:14 AM
to dwross

Thanks for the Tadaaki Tani quote - the two post-war references are a bit late but you prompted me to look again at the J.Opt.Soc.Am paper again and Mueller does quote reparations documents (R. Koslowsky and H. Mueller, Agfa Film Plant, Wolfen, Germany. Reports September-October 1936. Bibliography of Scientific and Industrial Reports (U. S. Department of Commerce, Washington), Vol. 8, p. 873. PB 70053, fr. 831-50.) as 'evidence for the use of gold salts in modern emulsion manufacture'. This is a Library of Congress microfilm I probably need to see. Tani seems to have published as recently as 2007 on gold and there seems to be some current research from China on gold for X-ray films but this - though interesting - is way off my beam.

Steigmann I know nothing about - I'm guessing much more recent than the 1940s/50s.

Thanks too for the UK patent number for the Ron Collins patent - I've found the US patent equivalent US2399083 - according to Hercock, R.J. & Jones, G.A. (1979) Silver by the ton: the history of Ilford Limited, 1879-1979. Collins reckoned that Koslowski had not found the idea time to add the gold salts - he favoured prior to digestion but after washing.

As I say I am trying to establish an evidence chain that Koslowski's work on gold was used by others in post-war production either for commercial or aerial reconnaissance emulsions - there's a solid and logical reason why Ansco had access to K's research but was the information news to Kodak? According to Collins it was certainly not news to Ilford.

to Photo Engineer
Thanks for posting in reply - Sheppard published in 1925 and Mueller cites Jenisch (1926) and Carol and Hubbard (1928) as attempting to push that research forwards with colloidal particles of gold and platinum. Having spoken with a couple of Kodak Harrow research scientists (now retired), their recall is that Kodak began to use S+Au sensitisation in the 1950s and felt there was some connection with the work done by Koslowski. Wether Kodak got this information from the reparations haul of Agfa documents, from analysing others' products or from pure research is interesting.

I hadn't appreciated the applicability to AgBrI emulsions only.

One intriguing snippet from the Hercock & Jones history of Ilford if that the RAF preferred Ilford emulsions for photo recon work and that Ilford was prevent from patenting one advance - I presume in emulsion chemistry - by the Ministry of Aircraft Production. This was apparently called Tetragam - I though it might be a mis-spelling for Tertragram (four letter word i.e. "gold") but I think I'm barking up the wrong tree. Could it refer to a tetragonal crystal structure and be some grain-shape improvement - an early tabular grain emulsion? Ring any bells?

To you both many thanks for the leads and ideas.

11-26-2011, 12:04 PM

Thanks backat'cha for sharing your research. Great stuff well worth a rainy day in the basement stacks of a University library!

Steigmann is a player you should probably look into. I've never been able to find out much about his personal story, but he researched and wrote extensively, much of it for German emulsion factories. His earliest writing I've seen is 1924. Fortunately, his favorite references are his own earlier publications -- makes him easy to backtrack. Unfortunately, he wrote much of the earliest stuff in German journals. He seems like he was rather full of himself, but it's possible that was justified. Anyway, interesting guy, and under-appreciated, I think, in photographic technology history. I'm always on the lookout for more info on him.

He presented a couple of papers at the 1959 Colloquium of Scientific Photography. "Peptized Silver Bromoiodide Emulsions of Negative Speed" speaks extensively of gold sensitization, but both papers have a number of citations (many by Himself) that you might have use for. Most are from the late 20s and early 30s. Scientific Photography--Proceedings of the International Colloquium Held at Leige 1959, Edited by H. Sauvenier, Pergamon Press, 1962.


Photo Engineer
11-26-2011, 12:09 PM
Burt Carroll was certainly using S+Au sensitization, but not in the form we know it today. You have pointed that out from his articles when he was at the NBS, but whether he knew at that time that Kodak was really using it and it what form had to wait until after he joined Kodak.

Confusion arises over the correct time to add the Au, and this was caused in the early days when active gelatins were in common use. They supplied the Sulfur and so the exact timing was "when?" because heat and Sulfur were already there! Here is the current sequence.

Precipitate nuclei > ripen or digest > growth + dopants > vAg adjust > wash > Sulfur + Gold + heat + time > spectral sensitization > finals (doctors) > coat.


Ripen = heat and allow grain changes with no solvent addition.
Digest = Ripen + Silver Halide solvent present
Dopant = some metal or organic compound that changes the emulsions properties
Finals or Doctors = anything that changes the properties of the melted emulsion or the coating
Sulfur = NH4SCN, NaSCN, KSCN, Na2S2O3, (NH4)2S2O3 alone or in combination
Gold = there are so many possible compounds I hesitate to mention just one!


12-14-2011, 01:56 PM
Hello P.E. and All,
I do not know the structure of Sands SDA3057 sensitizing dye. But I do know that, when residual dye solution is left to dry on an eyedropper or beaker, it turns bright gold in color. Of course this might be organic "fool's gold". But I wonder if gold is used as a component of color sensitizing dyes. I know that at least 2 other people who are regulars on this forum now own some SDA3057 for use inj their future emulsions.

12-14-2011, 03:43 PM
Hello P.E. and All,
...it turns bright gold in color. Of course this might be organic "fool's gold". But I wonder if gold is used as a component of color sensitizing dyes. I know that at least 2 other people who are regulars on this forum now own some SDA3057 for use inj their future emulsions.

Bill, at $300 + per gram for SDA3057... gold is really "fool's dye" :p

12-14-2011, 04:04 PM
Not when you are working on a True Passion !

12-15-2011, 04:17 AM
But I do know that, when residual dye solution is left to dry on an eyedropper or beaker, it turns bright gold in color.

I've been wondering about this as well - pinacyanol shows the same behavior. I assume this is some broadband fluorescence effect but have no idea why this occurs on dried layers.

12-15-2011, 02:58 PM
I've been wondering about this as well - pinacyanol shows the same behavior. I assume this is some broadband fluorescence effect but have no idea why this occurs on dried layers.

If I may ask, how do you use the pinacyanol? I've had a bottle (chloride) on my desk for a couple of months, taunting me -- just daring me to put it in something. I've got a couple of ideas, but if you've been there already, I'd love piggyback off your experience before I jump down the rabbit hole. Apologies if you've talked about this before.


12-16-2011, 03:02 AM
If I may ask, how do you use the pinacyanol?

Denise, I've used pinacyanol for photopolymers and AgX emulsions. With regards to AgX, most of my attempts related to Jeff Blyth's diffusion method. That's to say, I hardly did any sulfur/gold sensitization. Instead, I heavily relied on ascorbate reduction sensitization. I don't know what the situation looks like for more sophisticated photographic emulsions, but with crude red-sensitive holographic emulsions the combination of pinacyanol and ascorbate resulted in surprisingly good photo speed.

To come back to gold sensitization) Wolfgang Baier, Die Geschichte der Fotografie, mentions the work of Dr. F. Kropff, who was said to have done research on gold sensitization for Gevaert in the mid 1920s...

12-16-2011, 09:17 AM
Thanks much for the info. It's a little brighter down that rabbit hole. I doubt your emulsions are any more 'crude' than mine. I'm going to try to push my favorite emulsion's sensitivity up a notch. I got spoiled by summer emulsion speeds.

Photo Engineer
12-16-2011, 02:18 PM
Sands does not reveal the chemical structure of its dyes. No dye that I know of contains gold. Some special dyes are complexed with Osmium.


04-23-2012, 12:39 PM
PE, what would be an example of 1 or 2 gold compounds that would work with S+Au sensitization? Just curious to see how expensive this stuff is.

Photo Engineer
04-23-2012, 01:07 PM
KAuCl4 is commonly used.

It is used at 1/3 with sulfur.


04-23-2012, 01:25 PM
Thanks Ron. And since I've got you... what's a typical Iridium compound that's used to affect LIK (latent image keeping) & reciprocity characteristics? Just curious; can you tell I'm reading your book (http://stores.photoformulary.com/Detail.bok?category=Labware%2FBottles&no=990&param_referer=http%3A%2F%2Fstores.photoformulary.c om%2FCategories.bok%3Fcart_id%3D95991458%26categor y%3DLabware%252FBottles&searchpath=131324901)?

Photo Engineer
04-23-2012, 01:37 PM
Iridium is noted in the extensive Appendix telling you how to prepare the solution for use. It is not a simple matter of using Iridium Chloride. You must prepare the proper solution or it goes bad.

Also, note that the point of addition in the make is critical. That is mentioned in the book but T&E is the only way to find the optimum place. It is usually added during the growth phase.