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  1. #51

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    Quote Originally Posted by Photo Engineer View Post
    Now for finishing, you are using thiocyanate + gold. Here is the order of use timewise from early days to modern:

    Active gelatins > Allyl Thiourea > Thiourea > Thiocyanate > Sodium Thiosulfate

    Gold was used after about 1945 at Kodak with all of the above, but hypo was used exclusively for Sulfur sensitization since the 50s or 60s.
    Ron-- since you're discussing sulfur+gold again, I was wondering why there was such a progression in the use of sulfur compounds over the years. Any ideas as to why thiosulfate was not used from the beginning?

    Sheppard in his patent (#1623499) mentions that "sodium hyposulfite" can be used, but then immediately says that this compound is in name correct in the scientific sense and not the compound with the same name used by photographers which is sodium thiosulfate...

    By hyposulfite, if he means salts in the archaic system where it's sulfite (SO3=) but with one less oxygen (making SO2=), then (As taken from wikipedia): "However salts containing SO2= and the corresponding acid, hyposulfurous acid (H2SO2) are not believed to exist." - then what would he have been referring to?

    OK - I guess I can see it in my 1932 CRC Handbook - it has NaHSO2 and calls is sodium hyposulfite. But I think this is what is called sodium dithionite - not to be confused with sodium dithionate, Na2S206.

    So why did he miss thiosulfate in the original patent. He sure listed a lot of other compounds, it seems like thiosulfate would have been something to try, and something they had at hand, too.

  2. #52
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    Kirk;

    Since the discovery of sulfur sensitization hinged on discovery that a thiourea was causing it, there was a natural progression in use of heat degradable sulfur compounds. That is my only guess here. IDK why. I do know that formulas from the 40s and 50s used Thiocyanates and then moved to Hypo. Early ones used Thioureas.

    I do know (I think, in the back of my memory) that the Thiourea sensitizations were hard to control, and that there was something specific about sulfur + gold where hypo was used. That is it, just a hint of memory.

    PE

  3. #53

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    Jesus died for somebody's sins, but not mine! (patti smith)

    Ach hum!

    Ron, Kirk;

    You guys must be sleepier than I am.
    Somebody missed hypo, but it wasn't Sheppard!

    Ray
    Last edited by Ray Rogers; 09-04-2008 at 05:01 PM. Click to view previous post history.

  4. #54
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    Well, Agfa used Thiocyanate salts for quite a while but Kodak was converting to Hypo IIRC. IDK the precise timeline.

    PE

  5. #55

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    Quote Originally Posted by Ray Rogers View Post
    Somebody missed hypo, but it wasn't Sheppard!
    Is it in his first patent? If so, please point it out and then I'll agree with you that it was I that missed it.

  6. #56

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    Quote Originally Posted by Kirk Keyes View Post
    Is it in his first patent? If so, please point it out and then I'll agree with you that it was I that missed it.
    It was in the patent you quoted, with his notes about hypo.

  7. #57

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    It's Hidden View

    Quote Originally Posted by Ray Rogers View Post
    It was in the patent you quoted, with his notes about hypo.
    To suggest Sheppard missed hypo verges on being sacrilegious!

    However, the position attained latter on by hypo certainly is not reflected in the early published reports, and initally there was some confusion, and a different allocation of emphasis was given. As Kodak did the leg work, their understanding changed.

    (PM me if you can't find it)
    Last edited by Ray Rogers; 09-04-2008 at 08:16 PM. Click to view previous post history.

  8. #58

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    OK Ray - I see that I had not found an earlier patent. Thanks for pointing that out...

    1574994 (1926) DOES mention the use of thiosulfate as a sensitizer, but 1623499 (1627), the one I quited above, DOES NOT mention thiosulfate. And Sheppard goes on to make sure you know that he's not talking about thiosulfate as well.

    So why the difference in the two patents then?

  9. #59

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    Quote Originally Posted by Kirk Keyes View Post
    OK So why the difference in the two patents then?
    Ray - you seem to quote yourself in sequential posts. What's up with that. It confuses me to see you having a conversation with yourself...

  10. #60

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    Quote Originally Posted by Ray Rogers View Post
    It was in the patent you quoted, with his notes about hypo.
    I still missed in in the one I quoted I guess. And my buddy Google Patents doesn't find it when I search on thiosulfate either. Granted, google doesn'thave the best OCR.

    Can you please give me page and line number...



 

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