Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 68,702   Posts: 1,482,654   Online: 636
      
Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 27
  1. #11
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,712
    Images
    65
    One way to increase contrast without reformulating the entire developer is to increase pH. You can do this by adding a 10% solution of Sodium Hydroxide to the developer and using pH paper to test for the desired contrast.

    The down side is the need to test (but you would anyhow if you reformulated) and you would sacrifice developer stability. As pH goes up, stability goes down.

    PE

  2. #12
    Nicholas Lindan's Avatar
    Join Date
    Sep 2006
    Location
    Cleveland, Ohio USA
    Shooter
    Multi Format
    Posts
    2,372
    Images
    4
    Quote Originally Posted by Photo Engineer View Post
    Here is a quote from a patent reference ...
    benzotriazole ....are also unsatisfactory in respect to rustproofing abilities. ...
    That's probably a new low for a 'quoted expert source'. If you are quoting a patent for a corrosion inhibitor that is promoting itself as superior to the prior art - benzotriazole - what do think it is going to say? "Unsatisfactory to whom?" is the question to answer.

    Google "Benzotriazole rustproofing". Microencapsulated benz is used in naval paints, the benz is released when the paint is scratched and bonds to the exposed metal. It isn't usually associated with steel but with preventing corrosion and tarnishing on copper and silver.

    This is getting silly ... correspondence closed.
    DARKROOM AUTOMATION
    f-Stop Timers - Enlarging Meters
    http://www.darkroomautomation.com/da-main.htm

  3. #13
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,712
    Images
    65
    Nicholas;

    I did exactly that google search and the first thing that came up was that quote. I thought it rather amusing. And of course, from that POV in your post above, you are completely correct.

    Yes, it can passivate metals from forming metal salts. Isn't that somewhat what I described? I was being tongue in cheek though referring to the patent! The action in photography was not quite as you described though if you read my post.

    You said: "Benz forms a waterproof polymer when it contacts any metal and this keeps the developer from acting on the grain. Once the the developer starts acting the benz has less effect. " , and this is really quite incorrect. The actual reaction or action if you will is in my first post here. It appears that you couldn't get past the part that offended you. I'm really sorry about that.

    AAMOF, all 3 compounds I mention are also used as corrosion inhibitors on metals. The interesting difference here that you missed is that in the case of corrosion inhibition, the compounds prevent oxidation or corrosion of the metal to form a salt, and in photography, the 3 compounds act essentially on the salt to prevent formation of the metal (fog). Think about that.

    In photo engineering circles, benzotriazole is referred to BTW, as BTAZ.



    PE

  4. #14

    Join Date
    Aug 2005
    Location
    Earth
    Shooter
    Multi Format
    Posts
    1,560
    Quote Originally Posted by Photo Engineer View Post
    You can do this by adding a 10% solution of Sodium Hydroxide to the developer and using pH paper to test for the desired contrast.
    PE
    Now THAT is absolutely amazing!
    Could you be more specific as to how I can use pH paper to test for contrast?!!!

    Ray

  5. #15
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,712
    Images
    65
    Ray;

    Sorry, mistake.

    You use pH paper to test for the desired pH value and you test the adjusted developer for the desired contrast. Wow what an error. Thanks.

    However, once you establish the pH you want, then pH paper can be used to "test for the desired contrast".

    Thanks for the correction.

    PE

  6. #16

    Join Date
    Nov 2004
    Posts
    1,091
    Benzotriazole can be replaced by 10x its weight of Potassium Bromide,at least in some formulas.GW Crawley suggested replacing the original 50mg/L Benzo in FX-37 by 500 mg/L KBr, as the bromide is easier to dissolve.Presumeably the replacement works the other way round.

  7. #17
    BradS's Avatar
    Join Date
    Sep 2004
    Location
    S.F. Bay Area, California
    Shooter
    Large Format
    Posts
    3,921
    Quote Originally Posted by Photo Engineer View Post
    ...As pH goes up, stability goes down.

    PE
    Can you elaborate on this? I think I understand but, I want to make sure...in particular, what is meant by 'stability'?

    Is it the...hmmm, say the activity of the developer that is unstable over time (as in the shelf life time) ? Or, is it simply "photographic properties" generally that are unstable over time (again, I'm assuming storage time but, perhaps, even over the development time?)

    Let's take an example...

    Compare the published D-23 receipe to say, D-23 plus 5grams per liter Borax (I believe the Borax actually increases the ph in this case but could be wrong).


    tia.

    Brad.

  8. #18
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,712
    Images
    65
    Brad;

    Firstoff, the major change is due to absorption of CO2 from the atmosphere which drops the pH as the developer keeps. This is due to the following: Borate and Carbonate love to buffer in the range of about 9.5 - 10.5 depending on the mix you have going. More Borate or Carbonate don't change pH much, this would only change buffer capacity, so you need to add something like Sodium Hydroxide.

    Now, this increase takes us away from the buffer point of Borate or Carbonate, and so the developer is less stable from a pH (and therefore contrast) standpoint and our goal is higher contrast.

    To get a high pH developer, you use Trisodium Phosphate as buffer and this works at about 11 - 11.5, but then the developer is still not as stable as you want due to Carbon Dioxide in the air.

    That is about it, stability to pH changes is what I referred to, and since high pH is the element I suggested, you can retain activity simply by checking and adjusting the pH if it starts to drift. This is, in fact, what is done to control E6 color developer (pH ~11 with phosphate) and Kodachrome developers when they drift. They are essentially high contrast color developers that force the reversal development to completion.

    The high contrast B&W developer, D8, has almost 40 g/l of Sodium Hydroxide and it is loaded with Hydroquinone. Both are known as being able to yield high contrast results. It has however, low buffer ability when compared to most other developers.

    PE
    Last edited by Photo Engineer; 04-23-2008 at 05:29 PM. Click to view previous post history. Reason: Error.

  9. #19
    BradS's Avatar
    Join Date
    Sep 2004
    Location
    S.F. Bay Area, California
    Shooter
    Large Format
    Posts
    3,921
    Oh, I was over analyzing it (again). Thanks for the explanation.

  10. #20

    Join Date
    Jan 2005
    Location
    Boston, MA
    Shooter
    Multi Format
    Posts
    1,416
    This may sound very disappointing, but it is very difficult, almost impossible, to increase contrast and decrease density at the same time, with a same emulsion and exposure.

    Benzotriazole _may_ *slightly* increase contrast, but it only do so in the very lightly exposed areas (shadow in negative, highlights in prints) and not in the rest of the curves. If you use too much benzotriazole, what is most likely to happen is to require longer development time and/or greater exposure, without changing the curve shape much except for the toe region.

    Crawley did publish interesting formula and his commentaries on them. I have tested a number of antifoggants, desensitizing dyes and KBr in various contexts, but in my experience none of them is a magic bullet. The reality is that if you try to change one thing and you lose something else. In almost all cases, I got the best results by balancing the developing agents, sulfite content, and the pH, while keeping the KBr and other antifoggants well within the reasonable and normal range. In particular, I did not find any magical effect in using Pinakryptol green, Pinakryptol yellow and various derivatives of phenosafranine in developer solutions.

Page 2 of 3 FirstFirst 123 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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