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  1. #1
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    Clarifying sulfur and sulfur + gold treatment

    Old gelatins contained varying amounts of allyl thiourea, and this was finally discovered and refined out of gelatin making the first so-called inactive gelatins. The allyl thiourea could be added then in a carefully measured amount, but this meant that all old formulas (about pre 1950) were obsolete.

    These old formulas can be detected if there is no addition of a sulfur containing compound with heat treatment.

    Well, further experimentation showed that sodium thiocyanate and sodium thiosulfate did the same thing. It turns out that it was the heat + sulfur compound wich formed Silver Sulfide sensitivity specks on the surface of the crystal. (it is more complex than this but this is good enough here)

    Then, just before WWII, Agfa discovered that gold added to the sulfur would give even higher speed, but at the cost of lower contrast. This was learned from Agfa formulas after the war. It is the only item that Kodak (and the world) learned from Agfa formulas that was unknown to Kodak.

    This is the history, and now for the details.

    Sulfur is added at 3 mg/mole - 100 mg/mole of silver if the average crystal size is in the range of about 1 micron to 0.1 microns just to give an example. Gold is added at 1/3 of this rate, on average. So, as grain size goes up, the Sulfur or Sulfur + Gold goes DOWN!!!!!

    The emulsion is heated to 60 deg C and then the Sulfur or Sulfur + Gold is added and held for the correct time, usually about 30 minutes to 90 minutes determined by emulsion type. The emulsion is then chilled and stored for use.

    This treatment will add up to 3 - 5 stops to the emulsion speed, and 1 - 2 contrast grades depending on emulsion type. It works least well with pure chloride emulsions and best with bromo-iodide emulsions with others falling in between and requiring other addenda. See Jim Browning's matrix formula in another thread for an example.

    You can derive the exact amount of sensitizer to use directly from photomicrographs, otherwise you must determine it by experimentation using time and amount of sensitizer as your variables.

    Remember that hypo is the best, but decomposes in solution and therefore, your hypo solution should be made up fresh every month and should be kept refrigerated.

    I hope this helps.

    PE

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    Hyper Hypo

    Quote Originally Posted by Photo Engineer View Post
    Remember that hypo is the best, but decomposes in solution and therefore, your hypo solution should be made up fresh every month and should be kept refrigerated.

    I hope this helps.

    PE

    Hi Ron- I wish I had known you when I was working on the matrix film development. When we had Fotokemika make the film from my formulation, the first trials came out totally fogged (I mean BLACK!). I travelled over to Croatia, and sat with the emulsion chemist, and tried to think of what went wrong. We decided that there was too much hypo being added to sensitize. The amount was about 10 times the normal amount. We proceeded with the regular amount, and everything worked fine. After further scratching my head, I figured out that my hypo solution had slowly gone bad over the 3 year period I was making trial emulsions, and that caused my additions to slowly increase. Stupidly, I hadn't realized that the hypo solution was slowly going bad! It was a major snafu, causing much pain and expense. Experience is so valuable! Other than that problem, the emulsion scaled very well from 4L mixes to 100 L mixes.

    Regards - Jim

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    Thanks for this, PE.

    Just one thing... most og the 'old' formula contain a ripening stage anyway - do we add our sulphur compound at this point - or must it be a seperate step added onto the end of the process?

    Steve
    Steve

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    Steve;

    This step was commonly done after the wash step. So, old emulsions can be left to stand to that point in most cases.

    PE

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    Clarification on the Clarification

    I was re-reading this and related threads today at lunchtime and I am having trouble wrapping my head around how to make up the solution necessary to use for sensitizing. No doubt I'm making this much harder than it is by going through this in my head while I am supposed to be doing real work. Gotta get this off my mind.

    Let's assume for example, my usual batch contains 6g of AgNO3 ending up with about 150ml of emulsion. I want to use sulfur + gold at a rate of 3:1. Furthermore, I have data that tells me that the sulfur is sodium thiosulfate (Na2S2O3·5H2O) used at 3.8x10^-6 mole per mole Ag. I will also use Chloroauric Acid (HAuCl4) as a 1% (w/v) solution for the gold.

    - So, at 169.87 g/mol for AgNO3, that is 0.035 mol of Ag.
    - at 248.18 g/mol for Na2S2O3·5H2O, 3.8x10^-6 mol is 0.00094 or about 1mg.
    - and I would want 1.3x10^-6 mol HAuCl4 per mol Ag
    - so at 393.83 g/mol for HAuCl4 (assuming trihydrate) that would be 0.00049 or 0.5mg

    (Have I got it right this far?)

    OK. If I make up a 1% solution of thiosulfate (1g/100ml H2O) each ml contains 10mg (0.01g thiosulfate. Likewise for the gold chloride solution. If I add the Na2S2O3 and HAuCl4 to a solvent (H20?) in a ratio of 3 to 1 I have my 3:1 ratio. So let's say in 100ml total, I have added 3ml thisulfate solution and 1ml HAuCl4 solution.

    If I had a mole of silver at this point it would be simple enough, I suppose. But I have 0.035 mol of Ag. This is where I get stuck! I can use Denise's Steigman's formula because she says how to make and use it.

    What sort of a solution do you make? I'm lost.

    Thank you all for any help.....

    -- jason
    All this has happened before, and all this will happen again.

  6. #6
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    Well, here is the way I figured it.

    I used about 100 mg/mole of Sodium Thiosulfate Pentahydrate per mole of Silver. This works out to (64/248) x 100 or about 25 mg / mole of actual Sulfur. The amount of actual moles of Gold would then be about 8 mg / mole of Silver. But, my emulsion is 1 micron and the chart in the book suggests that this is way too much Sulfur and so it would be too much gold.

    How then did I come up with the quantities I used? Well, by trial and error. That is because each emulsion is a beast unto itself and the chart and text books are only guidelines.

    Also, I left gold out of the book because the emulsion can become much more complicated. This is because the chances of severe fog go way up as does the chance to get low contrast. Preventative measures can often be complex.

    So, not knowing anything about the emulsion you are working with, I suggest some experiments where you add a mix of your Sulfur + Gold at 3/1 ratio and try different levels for 1 hour at 50 C and see what happens. Then go from there.

    One thing is this, Steigman's formula is not Denise's, it is Steigmans! And, it was used by Agfa in the 30s and 40s and is mentioned in both the FIAT and BIOS reports. The actual current finishing (chemical sensitizing) solution is a closely guarded secret as I note in the example in the book. It is a mix of 3 ingredients, ratios unknown, and concentration unknown.

    I tried to keep this "first volume" as simple as possible. Perhaps in V2 I should compare S and S+Au?

    PE

  7. #7
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    I'm pretty sure Jason meant my adaptation of Steigmann's formula, rescued from the history dungeon and re-jiggered for contemporary usefulness. There is a lot of good information buried in the old literature.
    www.thelightfarm.com
    Dedicated to Handmade Silver Gelatin Paper, Film, and Dry Plates.

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    Tons of information in the old stuff. You get some of the best information by poking around the literature that came out just before Kodak et al came into existence and gobbled everything up. Obviously we know some of it has been proven incorrect but I think it is positively amazing what those guys knew!

    So, last night I worked the Steigmann's formula backwards and came up with the following in reference to the article Laboratory-Scale Photographic Emulsion Technique by Thomas T. Hill (9/1996) that D used as her source.

    The emulsion he shows (Full-Ammonia Bromide) is sensitized as:

    GOLD: 7.4x10-6 mol/mol Ag or ~3mg/mole Ag (as HAuCl4)
    SULFUR: 3.2x10-4 mol/mol Ag or ~24mg/mole Ag (as NH4SCN)

    The numbers seem plausible from what I have researched. Denise, PE et al, what do you think?
    And I am correct in understanding that Steigmann's sensitizes for both GOLD and SILVER, yes?

    What do we gain by using Na2S2O3 rather than NH4SCN, other than twice the sulfur?

    And, PE, when you say 3:1 for S to Au, you are talking about quantity not moles, right?

    Long post. Anyway, if I've got the numbers right I may have answered my own question.
    All this has happened before, and all this will happen again.

  9. #9
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    Jason;

    The 3:1 is in moles. I then convert to mg of X to moles of Silver or mg of Silver used.

    The Sulfur sensitization is based on the release of Sulfur from either Hypo or Thiocyanate. The Hypo releases Sulfur faster and so IIRC, Thiocyanate takes more time or higher temperatures to get to the same place as you do with Hypo. And what you lose is the fact that Hypo decomposes rather rapidly in plain water and so you have to mix it fresh every time you use it.

    Denise has a good example of the Steigmann's solution mixing and use taken from an article edited by Woody Thomas of EK. This is almost exactly that used by Agfa in 1945 for their high speed motion picture film as given in the BIOS and FIAT reports. What you have to do is make sure that the molar ration of Gold to Sulfur is 1:3, and then you must find out how much (approx) to use using the chart in the book and then you have to find the time and temp that is right for your emulsion. As I said above, the time and temp I suggest is 60 mins and 60 deg. If you fog, back off, but OTOH, TAI solution can help as well.

    Remember, as I have said many times, finishing (Chemical sensitization) is my weakest point here. I am by no means an expert in this topic. I do know that in the absence of the proper tools, this is very much trial and error.

    Best wishes.

    PE

  10. #10
    kb3lms's Avatar
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    Here is a link to the spreadsheet I used to figure out my numbers for anyone interested:

    https://www.dropbox.com/s/9ci0uxkssb...Steigmanns.xls

    Steigmann's solution mixing and use taken from an article edited by Woody Thomas of EK.
    Yep. Mostly the same information is also found in the SPSE Handbook.

    -- Jason
    All this has happened before, and all this will happen again.

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