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  1. #51
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    Thiourea is banned in some states in the US. Interestingly enough in some of those states, it is found as a natural product in many common wildflowers. The toxicity of thiourea has been under debate for quite a while and nothing seems to be done. I think that it is due to the fact that the results are not conclusive enough.

    PE

  2. #52

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    And it's been traditionally used in silver polish too. That said, chemical safety sources list it as a possible carcinogen.
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  3. #53
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    Quote Originally Posted by Kirk Keyes View Post
    The benzotriazole variation of Ansco 130 that I mentioned above certainly does change the tone of Ilford Warmtone FB paper, and much as you show in your scans above. No thiourea needed to make a nearly neutral paper considering how warm it is to start with.

    Could you take some color densitometer readings of some paper in your formula at Dmax and compare them to the same paper in regular developer so we can get an idea of the color shift?
    Unfortunately I have no access to a Densitometer, there's never been a tradition of photographers using them in the UK, outside professional colour labs.

    The shift we are looking for is past Neutral to a Blue black tone, Thiourea appears to be capable of doing this but there are organic alternatives.

    The work on Thiourea to give blue/black tones was by a British Photo-chemist C.E.K. Mees of Wratten & Wainwright, Kodak bought the company and he moved to the US to set up Kodak's Rochester Resarch Laboratories.

    Ian

  4. #54

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    Ian - If you want to send me some samples/step wedges, I'll read them and post results. Then we can compare with my modified Ansco 130 developer. PM me and I'll give you my address.

    By the way, I don't know why more people don't use color densitomety so they can better discuss these matters...
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  5. #55
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    Densitometry is useless unless it is comparative densitometry with a check and the experiment!

    PE

  6. #56

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    That's what I plan on!
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  7. #57

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    Phenyl Mercaptotetrazol in about 5-10 mg / l conc. of PQ gives a definite bluer tint than benzotriazole. It also makes the blacks a bit deper. I found out, that Forte Fortezo reacted with pepper grain with amounts over 8 mg/l conc. Nitrobenzimidazole is another agent, that makes the tone bluer.
    I bought my Phenylmercaptotetrazol at Organica in Wolfen, Germany.

    Best regards
    Gerhard

  8. #58

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    The Photographers Formulary had 1-phenyl-5-mercaptotetrazol last year. A percent solution, 100 ml bottle is what I bought. It was pretty inexpensive. I suspect they still have it. Email them and ask, as I can't find it on the web site.
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  9. #59
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  10. #60

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    I have mixed up a developer containing Potassium Iodide instead of Benzotriazole and will report back.

    Metol 4g, Sodium Sulphite 25g, Hydroquinone 12g, Sodium Carbonate 65g, Potassium Iodide 16g, water to make 1000ml.

    I intend to dilute 1+3 for the working solution to get in the middle of the Potassium Iodide content range suggested by Ian Grant.


    Tom.
    Last edited by Tom Kershaw; 04-17-2009 at 04:46 PM. Click to view previous post history.

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