Chemistry question - hydroquinone and ammonium thiosulfate

Discussion in 'B&W: Film, Paper, Chemistry' started by tkamiya, Jun 22, 2012.

  1. tkamiya

    tkamiya Member

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    I have a couple of questions about common B&W chemicals....

    What is residual hydroquinone and how is it different from hydroquinone? Can either be used to make developers? Are there any conversion necessary if a recipe calls for hydroquinone and I use "residual" type?

    Why is ammonium thiosulfate only available in 60% solution rather than powder?? For example, a recipe in "Way Beyond" book calls for 120 grams of ammonium thiosulfate. It does not say in what hydration. (anhydrous/monohydrate/etc) Many other recipe I've seen is the same way. Is this a convention that I'm not aware of?

    Can someone give me a hand?
     
  2. RalphLambrecht

    RalphLambrecht Member

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    i also wish aammonium thiosulfate would be available in powder more readily. howeverit shouldn't be too difficultto calculatehow much of the 60%solution is required to get the same effect as 120gof powder per liter
     
  3. Gerald C Koch

    Gerald C Koch Member

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    Ammonium thiosulfate is supplied as a 60% solution because the solid is unstable. 100 g of the solution contains 60 g of ammmonium thiosulfate. To convert this to liquid measure divide by the specific gravity of the solution ~1.33 g/ml.

    I have no idea what "residual" hydroquinone is. Where does this term appear?
     
    Last edited by a moderator: Jun 22, 2012
  4. tkamiya

    tkamiya Member

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  5. Ian Grant

    Ian Grant Subscriber

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    What is Residual Hydroquinone, never heard of it ? If you stick the term into Google it refers to thev Photoformulary and skin lightening :D

    It should mean the very slight residues of hydroquione left in an emulsion/paper base after processing.

    Ammonium Thiosulphate (cryst) is readily available in Europe it's not so much unstable as hydroscopic so attracts water and tends to end up as a sticky mess, so for commercial use it's usually sold as a solution.

    Ian
     
  6. desertrat

    desertrat Subscriber

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    Maybe the Formulary is calling it 'Residual' because it's coming from the bottom of the drum that they bought it in? Who knows? I bought a 100 gram bottle of Formulary Hydroquinone from Adorama less than a year ago. I don't remember how it was listed at their website, but the bottle is labeled Hydroquinone with no mention of Residual.
     
  7. Gerald C Koch

    Gerald C Koch Member

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    While the ammonium ion NH4+ has a chemistry similar to that of sodium and potassium ions this is only true in acid solutions. Thus a salt like ammonium chloride is stable in acid solution but begins to liberate ammonia gas when the pH of the solution gets above 7. When heated the solid dissociates into ammopnia gas and hydrogen chloride. Ammonium bicarbonate is used as a leavening agent beause it decomposes to ammonia, water and carbon dioxide at oven temperatures. Ammonium carbonate is so unstable that it does not exist at all. Solid ammonium thiosulfate slowly releases ammonia even at room temperature. As Ian points out it is also deliquescent absorbing water from the air and liquifying. This is why it is sold as a solution of known composition.

    Speaking about booms, ammonium nitrate makes an excellent explosive and will detonate spontaneously if a large quantity is allowed to become moist. This happened in Texas City in 1947 when a whole shipload (2300 tons) went up taking most of the town with it. At least 581 people were killed.

    I never buy anything from PF as I think their prices are too high and the purity of some their chemicals suspect. I buy developing agents and some other chemicals from www.techcheminc.com.
     
    Last edited by a moderator: Jun 22, 2012
  8. eclarke

    eclarke Member

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  9. nworth

    nworth Subscriber

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    The problem with ammonium thiosulfate is that it is hygroscopic - it aggressively absorbs water from the air. In a damp environment you may even get puddles of ammonium thiosulfate solution along with the solid material. That means that the problem with the solid is that you can't be sure of just how much you have when you weigh it out, unless you keep it in a desiccator.
     
  10. tkamiya

    tkamiya Member

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    Understood on ammonium thisulfate....

    Any ideas on Residual hydroquinone? Googling is the first thing I did and I, too, found all kinds of references to making some kind of creme. So I take it, this is not a proper or even common chemical name.... Very strange.
     
  11. Ian Grant

    Ian Grant Subscriber

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    Adorama sell PF Residual Hydroquinone yet it's not on the Photo Formulary website. Very strange and as we've nboth found it's being sold as skin lightener, as such it's potentially quite dangerous as well.

    Ian
     
  12. hrst

    hrst Member

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    Hydroquinone is used in skin-whitening creams at about 2-3%... It has nothing to do with this mysterious "residual hydroquinone", it's just that some DIY people seem to have found this oddly named product and want to make their own HQ skin creams, as some ready-made HQ skin creams are quite expensive, apparently.

    My guess is that this "residual" thing is just some mysterious typo on Photoformulary product listing and nothing more... Photoformulary is well known for a bit... clunky marketing and website :smile:.

    It is interesting how some people are ready to apply a "developer" to their skin directly for long contact times and repeatably every day, while, at the same time, there are people who are afraid of even trying to develop photographs because they are so scared of these chemicals.

    I use this skin cream as an example to show people that they don't need to be that afraid; just be normally careful. If you get one drop of a developer to your hands, which happens every now and then when developing papers, and wash it out, it is still less than one of the millionth of the exposure thousands of people get on purpose without evident problems.
     
  13. tkamiya

    tkamiya Member

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    I did the sensible thing... just sent an email off to an Adorama rep for clarification. According to the manufacturer's SKU listed, and cross referencing it to PF site, it appears to be just a regular hydroquinone.

    Apparently, people use residual hydroquinone, whatever it is, to make skin whitening cream. I wonder if they have to bathe in fixer to make that permanent? Looking at MSDS, this stuff isn't entirely harmless at higher concentrations....
     
  14. Gerald C Koch

    Gerald C Koch Member

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    Vanity of vanities, all is vanity. It is amazing what people will do with the belief that they are becoming more beautiful. The folllowing is from the hydroquinone MSDS.

    "Skin: May cause skin sensitization, an allergic reaction, which becomes evident upon re-exposure to this material. May cause dermatitis. Causes redness and pain. May be harmful if absorbed through the skin. Repeated exposure may cause hyperpigmentation of fair skin and depigmentation of dark skin. Causes skin irritation and possible burns. Substance is readily absorbed through the skin.
     
  15. tkamiya

    tkamiya Member

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    ....and if 2% works well, 50% ought to work 25 times better :blink:
     
  16. tkamiya

    tkamiya Member

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    I heard back from Adorama. "Residual" was in error. It's the usual hydroquinone.