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  1. Sean Guest

    A Black&White Reversal Process In Memory Of Agfa Scala 200x

    4 Comments by Sean Published on 10-28-2006 09:17 PM
    The fogging redeveloper recipe has now moved into a reversal recipe to present it in the entire context. http://home.snafu.de/jens.osbahr/pho...r_reversal.pdf
    Last edited by Hans Borjes; 04-15-2007 at 03:49 AM. Click to view previous post history.

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  3. #2
    Sean's Avatar
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    Comments from previous article system:

    By gainer - 04:09 PM, 05-18-2006 Edit Rating: None
    Just curious. Is stannous fluoride any less hazardous than the chloride? I'm asking because I have a stannous fluoride mouthwash that I spit down the drain. It's about 0.6% solution, which means the whole bottle is about 3100 mg. There is no warning of any kind on the label about proper disposal.

    Maybe the fluoride would work as well?
    By Tom Hoskinson - 01:58 AM, 05-19-2006 Edit Rating: None
    It is not a good idea to ingest a significant amount of either Tin Chloride or Tin Flouride.

    Tin chloride is a reducing agent: For example, SnCl2 reduces quinones to hydroquinones. See: http://en.wikipedia.org/wiki/Stannous_chloride

    Tin Flouride is primarily used as a flouride source in toothpaste and is also used in water flouridation systems and in anodizing chemistry. I did not find any references to photographic chemistry applications.
    By gainer - 04:59 PM, 05-19-2006 Edit Rating: None
    I used to use tin chloride as a soldering flux in my other life as a repairer of musical instruments. I doubt you can buy it for that purpose any more. I don't remember if it was stannous or stannic.
    By Tom Hoskinson - 12:05 AM, 05-21-2006 Edit Rating: None
    Pat, my guess is Stannous Chloride (SnCL2). Stannic Chloride is pretty nasty stuff

    Tin(IV) chloride, also known as tin tetrachloride or stannic chloride is a chemical compound with the formula SnCl4. At room temperature it is a colourless liquid, which fumes on contact with air, giving a stinging odour. It was used as a chemical weapon in WW-I

    http://en.wikipedia.org/wiki/Stannic_chloride
    By Tom Hoskinson - 12:46 AM, 05-21-2006 Edit Rating: None
    My Colgate TOTAL Clean Mint Toothpaste contains Sodium Flouride, with the following warning: If more than is used for brushing is accidentally swallowed, get medical help or contact a poison control center right away.

    However, Colgate doesn't tell me how much I need to feed to a lab rat to ensure a fatal outcome...
    By gainer - 11:46 PM, 05-21-2006 Edit Rating: None
    It figures that stannous chloride would be a soldering flux, as the purpose of flux is to reduce oxidized metals. I think the sodium hydrosulfite sold in super markets as Iron Out will do the same, but I think it will work without the developer. I'll have to try it.
    By Gerald Koch - 03:52 PM, 05-24-2006 Edit Rating: None
    Tin salts are not particularly toxic which is why tin is used in tin cans.
    By Donald Qualls - 01:47 AM, 06-01-2006 Edit Rating: None
    Gainer, I've been referred to Iron Out as a stand-along fogging redeveloper by PhotoEngineer. Dunno what the grain will wind up like, though; I found with my Tri-X processed in reversal that changing the second developer from Dektol (parallelling the Ilford recommended Bromophen) to HC-110 made a *huge* difference in the grain in the final transparency. Cheap enough to find out, I guess...
    By psvensson - 04:31 PM, 06-01-2006 Edit Rating: None
    The PDF in insteresting, but AFAIK the warning against cyanide release from thiocyanate is unnecessary. As I've learned from a flame war on photo.net, it takes high heat, in addition to acid, to liberate cyanide from thiocyanate.
    By gainer - 05:28 PM, 06-01-2006 Edit Rating: None
    I used thiocyanate in the form of Kodak stabilizer a lot many years ago. Certainly you don't want to drink the solution, but it's not going to jump out and grab you either.

  4. #3
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    By pnance - 05:22 PM, 06-02-2006 Edit Rating: None
    Tom: the msds says: Anhydrous: Oral rat LD50: 700 mg/kg.
    Say, wouldn't that be 140 lb for an LD50 to a 200 lb human (assuming equal morbidity rates?) that is dangerous. Try not to ingest more that a hundred pounds!
    By Photo Engineer - 05:43 PM, 06-02-2006 Edit Rating: None
    It is simply not true that thiocyanate produces cyanide on contact with acid!

    This mistaken impression has misled a lot of people.

    Heating thiocyanates or treating them with acid does not produce a toxic gas.

    I am tired of this myth.

    PE
    By Hans Borjes - 07:47 PM, 06-02-2006 Edit Rating: None
    I am not too sure about an 'official' source for MSDS. A source that I would consider reliable is Merck, a big manufacturer of chemicals in Europe. Their datasheet says: 'Entwickelt bei Berührung mit Säure sehr giftige Gase.', i.e. 'develops very toxic gases on contact with acids'.http://chemdat.merck.de/pls/pi03/we...p;s=&lang=1
    By Photo Engineer - 08:11 PM, 06-02-2006 Edit Rating: None
    Hans, my sources are severalfold.

    1. The Merck index which in the US edition says no such thing about the liberation of toxic gas or any severe toxicity of any common thiocyanate salt.

    2. My own chemical training and experience and textbooks here at hand, along with the comments by other chemists I have talked with to isure that my comment above is accurate.

    AAMOF, the Kodak C41 RA fix contains a high level of thiocyanate, and if you will check the MSDS on Kodak's web site you will see that this is correct. There are no special precautions listed for this fixer. It is used in many minilabs all over the world.

    I believe that this is a self replicating myth that has taken on a life of its own. I am sorry that this has taken place.

    PE
    By Photo Engineer - 08:58 PM, 06-02-2006 Edit Rating: None
    I have continued my research and find that there are conflicting statements on the internet, but consistant statements in the textbooks I have.

    Here, the data seems somewhat in line with the data I have:

    http://www.physchem.ox.ac.uk/MSDS/P...hiocyanate.html

    with no comment other than skin problems, and the comment to avoid nitric acid.

    But, here:

    http://ptcl.chem.ox.ac.uk/~hmc/hsci...hiocyanate.html

    the data is much more damning, however if one digs deeper, the data says that the LD50 for Potassium Cyanide is 10mg/Kg. It says that for Potassium Thiocyanate it is 590 mg/Kg or more than 50 times greater. It also says that the thiocyanates were once useful as hypotensives.

    In other words, these are two "chemicals that create very toxic gases in contact with acids" if one believes the internet reports, but if one searches more deeply one finds that one is always a poison and fatal just by contact with stomach acids, whereas the other can be used as a phamaceutical at the right dose.

    For comparison, the LD50 for sodium chloride is 3.75 g/Kg, or about 8x that of Potassium Thiocyanate.

    Source is Merck Index, 12th edition.

    PE
    By Hans Borjes - 10:10 PM, 06-02-2006 Edit Rating: None
    The link I posted above did not work very well. This one does:
    http://chemdat.merck.de/documents/s...1051/105124.pdf

    Should I go and try? If I don't post tomorrow, then it does produce toxic gas... ;-)

    Just kidding.
    By Photo Engineer - 11:23 PM, 06-02-2006 Edit Rating: None
    Hans, thanks, I've read all of this and more over the years. Here is more information.

    If you are poisoned by cyanide, the antidote is sodium thiosulfate (hypo) injected into the blood, and what it does is convert the cyanohemoglobin in the blood into thiocyanates.

    PE
    By Jordan - 03:17 AM, 06-04-2006 Edit Rating: None
    There's definitely no risk of releasing HCN from dilute acid solutions of KSCN (including stop baths, etc.) That carbon-sulfur bond is quite strong. I <i>have</i> decomposed organic isothiocyanates before, but in aqueous base. H2S was one of the products, and I presume the others were NH3 and CO2.
    By Gerald Koch - 07:14 PM, 06-07-2006 Edit Rating: None
    Heat is not going to release hydrogen cyanide either. Years ago mercury thiocyanate mixed with a little gum arabic was sold as a parlor trick called Pharoh's Serpents. Each *egg* when touched by a match flame created a copious amount of ash in the shape of a coiled snake. Nobody died from breathing the smoke generated.
    By Gerald Koch - 03:57 PM, 06-09-2006 Edit Rating: None
    If you read the literature cited above the hazardous decomposition product that is mentioned is NOT hydrogen cyanide but rather hydrogen sulfide.

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    By Hans Borjes - 10:46 PM, 06-09-2006 Edit Rating: None
    Sorry for the confusion, I am a software engineer, not a chemist. BTW, the document was updated to include test frames now. I would be glad to hear technical comments about the process itself.

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    The document now contains densitometric data.
    There is nothing like Scala? There are various alternatives!
    http://www.apug.org/forums/forum228/...cala-200x.html



 

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