Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,338   Posts: 1,537,650   Online: 984
      
Page 27 of 55 FirstFirst ... 172122232425262728293031323337 ... LastLast
Results 261 to 270 of 550
  1. #261
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,972
    Images
    65
    If you run a keeping test of the dilute working solution, you will see how it performs with your tap water. By having a few volunteers run a similar test, we will learn a lot.

    PE

  2. #262

    Join Date
    Nov 2004
    Posts
    1,136
    Mark,

    I don't know of any developer produced on a non-profit basis that contains a chelating agent to prevent hard water cloudiness.This includes all Crawley's published formulae, PMK Pyro,the Pyrocats. Gainer's PC-TEA etc.I have not come across any grumbles on the internet about cloudiness produced by these developers.My guess is that manufacturers include a chelating agent because it is easier to sell a developer that produces a clear solution in hard water.So IMO chelating agent is interesting but not necessary in a non-profit developer.

    I once wrote to Geoffrey Crawley re glycol in developers and he replied IIRC that he put some in his commercial developers to help prevent freezing in winter,evidently he considered glycol not harmful to the developing properties.

    Re metaborate and TEA , IMO it would be interesting if a recommended non-crystallising metaborate formula could be found for those who only have metaborate not TEA.But at this time your work does seem to suggest that TEA might turn out to give a result closer to Xtol if this line is pursued.

  3. #263

    Join Date
    Apr 2008
    Location
    Escondido, California, USA
    Shooter
    35mm RF
    Posts
    654
    Quote Originally Posted by Photo Engineer View Post
    If you run a keeping test of the dilute working solution, you will see how it performs with your tap water. By having a few volunteers run a similar test, we will learn a lot. PE
    I'll need to do that. My intention is to make the dev last more than 45 minutes with hard water before it gets cloudy. It would be nice if it could sit around for a few hours or a day. The wikipedia article on citric acid here says it's an "excellent" chelating agent. But PE says there are much better choices around (Kodak likes DTPA). I guess we don't know if citric acid will chelate well in a developer, so as PE says, tests must be run. Also, I understand that the Fenton reaction with iron will eventually destroy the ascorbate, but that takes days or weeks, and this is a one-shot dev, so I don't care about Mr. Fenton. Although if I can chelate the iron for free, I will.

    Rudi, thanks for the link to the list of stability constants. There's much useful data in there. I just looked up Glycine and decided it would be pretty weak.

    Mark Overton

  4. #264

    Join Date
    Apr 2008
    Location
    Escondido, California, USA
    Shooter
    35mm RF
    Posts
    654
    Quote Originally Posted by Alan Johnson View Post
    I don't know of any developer produced on a non-profit basis that contains a chelating agent to prevent hard water cloudiness.This includes all Crawley's published formulae, PMK Pyro,the Pyrocats. Gainer's PC-TEA etc.I have not come across any grumbles on the internet about cloudiness produced by these developers.
    I hadn't thought of that, and thanks for pointing it out. Maybe such folks typically use distilled or DI water. Anyway, it's an easy test, so I might as well check if all that citric acid prevents cloudiness.

    Is 99% TEA hard to obtain in the UK? This subject was brought up a few months ago, and I don't recall a clear conclusion. Does Mistralni sell 98% TEA? I think you can get it at Fototechnik Suvatlar in Germany. In the US, 99% TEA can be purchased from The Chemistry Store. For consistency, I suggest avoiding the 85% TEA sold by the Formulary.

    A few months ago, PE wrote "...buffer capacity can be looked at as the total number of moles of alkali present in a solution." TEA is an alkali, and when used as the main solvent, it contributes a large number of moles and therefore should boost buffer capacity greatly. That's a strong advantage.

    Today's Experiment -- reducing viscosity of TEA by mixing in PG:

    I wanted to see how much propylene glycol (PG) needed to be mixed into TEA to get acceptable viscosity at cool temperatures. A water-bath kept temperature at 17C, simulating a cool darkroom in winter. A 28%-72% mixture of PG-TEA had reasonable viscosity at 17C. Dissolving powdered chemicals will boost viscosity a little, so I'd say 33%-67% (one third / two thirds) of PG-TEA would work well.

    Mark Overton

  5. #265
    Rudeofus's Avatar
    Join Date
    Aug 2009
    Shooter
    Medium Format
    Posts
    1,620
    Images
    10
    Quote Originally Posted by albada View Post
    The wikipedia article on citric acid here says it's an "excellent" chelating agent.
    Heavy Fuel Oil is a "great" fuel but I still wouldn't recommend it for your car. When I cleaned limestone residues from my sanitary installations with citric acid, it worked great, but at a temperature, pH level and concentration you would not want in your developer. My recommendation is you take the hardest tap water you can find (let some limestones sit in it for a week), add the amount of citric acid you use in you dev to this water, then add 100 g/l sodium carbonate. If you get precipitation, you likely need a stronger chelating agent.
    Quote Originally Posted by albada View Post
    I guess we don't know if citric acid will chelate well in a developer, so as PE says, tests must be run. Also, I understand that the Fenton reaction with iron will eventually destroy the ascorbate, but that takes days or weeks, and this is a one-shot dev, so I don't care about Mr. Fenton. Although if I can chelate the iron for free, I will.
    I have read reports that Mr. Fenton sometimes takes days or weeks to do his job, but sometimes he is in a superhurry and finishes off all the ascorbate in an hour or so. Therefore I think you should pursue one of two options:
    1. Distilled water is easier to get than most chelating agents, and quite cheap, too. Note, that your concentrate targets people who are very low volume developers, so the cost of distilled water should be irrelevant. If one roll of film fails due to evil Mr. Fenton, it's a pitty but most likely the damage done to humanity is of limited extent. Few pieces of great art come from a tiny portfolio.
    2. Or use a chelating agent which takes care of all these issues (tap water impurities, iron) at once. If DTPA does not dissolve in the concentrate, you might mix it with the sulfite. Maybe Dequest 2010 does dissolve in PG and works well
    Trying to be the best of whatever I am, even if what I am is no good.

  6. #266

    Join Date
    Nov 2004
    Posts
    1,136
    Quote Originally Posted by albada View Post

    Is 99% TEA hard to obtain in the UK? This subject was brought up a few months ago, and I don't recall a clear conclusion. Does Mistralni sell 98% TEA? I think you can get it at Fototechnik Suvatlar in Germany. In the US, 99% TEA can be purchased from The Chemistry Store. For consistency, I suggest avoiding the 85% TEA sold by the Formulary.



    Mark Overton
    I have not found a source of relatively pure and inexpensive TEA in the UK.
    Mistralni.co.uk is not expensive but is the 85% grade.
    Scichem.com sell 500ml 97% grade at GBP 16.07+VAT + ~GBP 12 shipping but need an email request stating what it is required for and details of the buyer whereupon they will decide to supply it or not.

    BTW, I don't think a little cloudiness does any harm,I always get it from the carbonate in Pyrocat-HD with no apparent harmful effect.

  7. #267
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,972
    Images
    65
    Cloudiness, from a precipitate by hard water, can cause defects in the image of films. The small particles become lodged in the gelatin causing you to have specks of white in the final print.

    PE

  8. #268

    Join Date
    Nov 2004
    Posts
    1,136
    "Sequestering agents are not photographically inactive under all circumstances"-FDC p123.
    Because Xtol concentrate is diluted 1+49 the ratio of sequestering agent concentration to phenidone and ascorbate concentration will be much higher than in Xtol if the same agent concentration is present in the working solution to prevent cloudiness.

  9. #269

    Join Date
    Apr 2008
    Location
    Escondido, California, USA
    Shooter
    35mm RF
    Posts
    654
    Quote Originally Posted by Rudeofus View Post
    Distilled water is easier to get than most chelating agents, and quite cheap, too. Note, that your concentrate targets people who are very low volume developers, so the cost of distilled water should be irrelevant.
    That cheap distilled water will eliminate cloudiness. That leaves the Fenton reaction. But the amount of iron will be low, sourced mainly from the sulfite and not from iron pipes, so Fenton's destruction of ascorbate shouldn't be an issue either. So I'm thinking I'll follow Alan's idea and say "if your tap water is hard, use distilled water" and ignore chelation because it won't be an issue for this one-shot brew.

    Anyway...
    While investigating chelation of iron, I noticed that your link to the table of stability contants shows that:

    * Citric acid chelates Fe(III) well, and Fe(II) poorly.
    * Salicylic acid chelates Fe(II) well and Fe(III) mediocrely (if that's a word).

    Could both be used and get good chelation of all iron? These acids have the advantage of being widely available.

    Mark Overton

  10. #270
    Rudeofus's Avatar
    Join Date
    Aug 2009
    Shooter
    Medium Format
    Posts
    1,620
    Images
    10
    Quote Originally Posted by albada View Post
    So I'm thinking I'll follow Alan's idea and say "if your tap water is hard, use distilled water" and ignore chelation because it won't be an issue for this one-shot brew.
    If you still have space left in your instruction manual, you can add the line "and those whiners, for whom distilled water is completely unavailable for whatever obscure reasons, are encouraged to boil their hard tap water before using it to mix developer".

    Boiling water drives out CO2, which in turn reduces the amount of HCO3- while leaving CO32-, which leads to precipitation of CaCO3, as frequently observed in water heaters of all kind.
    Quote Originally Posted by albada View Post
    * Citric acid chelates Fe(III) well, and Fe(II) poorly.
    * Salicylic acid chelates Fe(II) well and Fe(III) mediocrely (if that's a word).

    Could both be used and get good chelation of all iron? These acids have the advantage of being widely available.
    If you look at the numbers, you'll see that Salicylic chelates FeII better than Citrate (6.55 vs. 3.2), and it also chelates FeIII better than Citrate (16.35 vs. 11.85). If you have Salicylic Acid in your dev, you won't need Citric Acid any more. Note that chelate stability does not tell the whole story since EDTA, which is a strong chelating agent for both FeII and FeIII, is known to accelerate the Fenton reaction.

    Note that Salicylic Acid is not overly soluble (Wikipedia says 2g/l), so you may have to add some other acid anyway to get the pH you want. At 1g/l is is said to keep DS-10 stable, a developer you might remember
    Trying to be the best of whatever I am, even if what I am is no good.



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin