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  1. #1
    JOSarff's Avatar
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    Sulfur and Gold sensitation

    I recall a posting about sulfur and gold sensitation that PE said should be around 3:1.

    On the light farm website they use Steigmann standard aurous ammonium thiocyanate solution (50ml ammonium thyocyanate 1% and 6ml gold chloride solution 1%) which is about 8:1. Is this "strong enough" or a comprimise because of increased fog with increased gold?

    It's in the section on glass plate emulsions.

    Thanks all
    Joe

  2. #2
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    Joe;

    The 8:1 is from older work and also uses thiocyanate. These two differences make up for what I said which is based on gold choride and sodium thiosulfate pentahydrate. The ammonium ion also has a fairly substantial effect on the final outcome. This all assumes 100% oxidized gelatin. There are only two sources of this product. One is Kodak and the other is Roussellot. The Formulary sells the Kodak product.

    PE

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    So the Steigmann formula was from the time of active gelatins - it needed less sulfur than what phthalated gelatin of today would need as the active gelatin already had sulfur in it?

    One of the books I have, I forget which, has a nice graph showing the speed increase from gold alone and sulfur alone and the two combined. Sulfur alone was more effective than gold alone, but the two combined with much better than either alone.

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    Yes, the Steigman formula was used during the crossover, IIRC. Sulfur increases contrast and speed, gold increases speed and the combination amplify both speed and contrast. This is a general rule of thumb. Gold has a tendancy to give a soft toe while increasing speed. The combination is often foggier than just sulfur alone.

    Selenium and Tellurium have also been used, but are so toxic that Kodak has abandoned their use. Fuji uses Tellurium for super sensitization of emulsions.

    PE

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    Kirk:

    First, congratultions to you and Denise on the great workshop last weekend. I was sorry to miss it.

    If you run across those graphs I would love a copy.

    Joe

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    Quote Originally Posted by JOSarff View Post
    Kirk:

    First, congratultions to you and Denise on the great workshop last weekend. I was sorry to miss it.

    If you run across those graphs I would love a copy.

    Joe
    Hey Joe,
    How do you know that the Workshop was "great" as you weren't there?
    (It was great. A lucky guess on your part?)
    Bill

  7. #7

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    Joe,

    I just looked and it's Neblette's Eight Ed. "Imaging Processes and Meterials" from 1989. Nice 3-D graphs showing the relationship between gold and sulfur, both for cubic and octahedral crystal habits.

    It also has a really nice discussion on t-grains and pAg as well.

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    Here are the data

    The data below assumes the use of KAuCl4 and Na2S2O3.H2O for sensitization:

    The data are stated as gold/sulfur in milligrams / mole of silver

    1/3 for 1.0 micron grains
    5/15 for 0.5 micron grains
    35/100 for 0.1 micron grains

    The attached chart shows the relationship to the vAg and the crystal habit that is formed. From this, you can see that my crystals in the second attachment are made at a vAg value between 7.5 and 8. The extreme rounding is due to the ammonia used to digest (grow) the crystals, and if taken much further the crystals would be nearly spherical.

    PE
    Attached Thumbnails Attached Thumbnails crystal diagram.jpg   Electron  micrograph - BrI SRAD.jpg  

  9. #9
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    Bill:

    Good hearing from you. There was a rather large post in the workshop section by Don12x20 praising both Denise and Kirk for the workshop and information, and your presentation also. Melody also mentioned it when I was over at B&S to pick up a cup of KI.

    Joe

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    Finally some time to get back to this...

    PE makes a good point about the amount of gold or silver being based on the average diameter of the halide crystal.

    The Neblette's book I referenced above discusses how the amount of Au and S are related to the crystal habit as well. It says that for AgBr crystals, cubic crystals are more sensitive to the amount of gold, while the octahedral crystals are more sensitive to sulfur concentration.

    It also says that octahedral emulsions gain about 0.7 log E in speed for sulfur-only but only about 0.4 log E for gold only. The reverse was true for cubes - they gain about 0.9 log E in speed for gold-only and about 0.4 log E for sulfur only.

    The graphs they reproduce also show this effect - for the AgBr octahedral, the optimum Au/S amount was about 1.6 mg/mole Ag sulfur and the speed kept increasing as the concentration of gold was increased. The graph shows an optimum ratio at about 2.0 mg gold/mole Ag and 1.6 mg sulfur/mole Ag. However, as was just mentioned, the speed does keep increasing as the gold concentration increases as it goes off the graph at 2.25 mg Au/mole Ag.

    For AgBr cubes, there is a maximum speed gain for the ration of gold concentrations from 1.0 to 2.0 mg Au/mole Ag and 1.4 to 3.0 mg sulfur/mole Ag.

    So I guess you could use the chart PE shows to figure out which crystal habit you are making to determine what ratio of Au and S to use.

    Kirk

    Also, PE - with all your talk of pAg lately, perhaps you should write your handle as "pE"...

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