Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,572   Posts: 1,545,655   Online: 969
      
Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 26
  1. #11
    eclarke's Avatar
    Join Date
    Jun 2004
    Location
    New Berlin, Wi
    Shooter
    ULarge Format
    Posts
    1,953
    Images
    71
    Agreed that there's no holy grail, but it's nice to be able to discuss things like developers when Ihave had hands on experience with it and not merely parrot something so,ebody else wrote. I like to tinker so I can rule things out and be able to give real info about my results. As an example, I use a nice Gitzo carbon tripod with an Arca Cube and it's a spectacular setup yet I get flamed by people about using an expensive combination. The flamers have mostly never even seen it, let alone used it. The same thing happens with developer talk. I get flamed for the Germain because everybody says he was sort of a quack and I should use Edwal 12..but...I've developed several thousand sheets in Germain's Finegrain and it's still my favorite for all films..Thanks for the input, I'm just going to dispense with the sulfuric and adjust the pH at the end. Won't be the first liter of developer I have thrown away or I might like it!! EC

  2. #12

    Join Date
    Jul 2010
    Location
    Southern USA
    Shooter
    Multi Format
    Posts
    3,844
    Gradol was paraminophenol hemisulfate. A curious choice since its keeping property in solution a less than for Metol.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  3. #13
    eclarke's Avatar
    Join Date
    Jun 2004
    Location
    New Berlin, Wi
    Shooter
    ULarge Format
    Posts
    1,953
    Images
    71
    "Gradol was paraminophenol hemisulfate" There's the answer, and maybe what the sulfuric acid is about. I think this might be a dead end.. Thanks..Evan

  4. #14

    Join Date
    Jun 2009
    Location
    Odessa, UA
    Shooter
    35mm
    Posts
    234
    PAP base isn't soluble in water at neutral or low alkali pH. I think that Sulfuric Acid in Edwal-20 formula allow PAP base dissolved in water at acidic pH

  5. #15
    Rudeofus's Avatar
    Join Date
    Aug 2009
    Shooter
    Medium Format
    Posts
    1,653
    Images
    10
    I remember I read about some biology book where the average length of some kind of bird was specified as 30.48cm. In the same way I would guess that nobody measured the volume of Sulfuric Acid to four digits (and I'm not entirely sure how exactly one would do this anyway), but that instead some simple number was converted to a different system of measurements. Looking at the other rather odd amounts in the recipe would also suggest this theory.
    Trying to be the best of whatever I am, even if what I am is no good.

  6. #16
    Ian Grant's Avatar
    Join Date
    Aug 2004
    Location
    West Midlands, UK, and Turkey
    Shooter
    Multi Format
    Posts
    16,276
    Images
    148
    The keeping properties of a developing agent can be greatly incresed by the addition of another. It might sound surprising but Ilford sold D&P tank developers with Metol, Hydroquinone and Pyrogallol, designed for high volumes and replenished. The Pyrogallol acts as an oxygen scavenger.

    PPD also forms a complex with some developing agents, the most common being Meritol which is a PPD/Pyrocatechin complex. It may well be less toxic as a complex although the commercial developers I used which cointained Meritol did have a warning label even in the late 1960s.

    Womens (and the odd vain mans) hair dyes use(d) PPD derivaties, most have changed to safer compounds but not everywhere.

    Some of these developers gave exceptionally good results and in a way they were the magic bullets when they were first introduced. Modern films are less affected in terms of fine grain by choice of developer, old style films though could give grain like golf balls with the wrong type of developer and excellent fine grain in one of these off beat fine grain developers, far better than most fine grain developer from Kodak, Ilford Agfa etc.

    As to why p-aminophenol in a low pH developer well Ilford used it alongside Metol in their early super fine grain developer sold in the 1930's.

    Ian

  7. #17
    eclarke's Avatar
    Join Date
    Jun 2004
    Location
    New Berlin, Wi
    Shooter
    ULarge Format
    Posts
    1,953
    Images
    71
    Thanks, Ian..

  8. #18

    Join Date
    Jul 2010
    Location
    Southern USA
    Shooter
    Multi Format
    Posts
    3,844
    Quote Originally Posted by Ian Grant View Post
    PPD also forms a complex with some developing agents, the most common being Meritol which is a PPD/Pyrocatechin complex. It may well be less toxic as a complex although the commercial developers I used which cointained Meritol did have a warning label even in the late 1960s.
    Another compound is between ppd and hydroquinone. This is a 1:1 addition compound where one ppd molecule sits on a hydroquinone molecule something like the two slices of bread in a sandwich. These compounds are held together by hydrogen bonds. While they are stable in solid form they dissociate back to ppd and hydroquinone or catechol when dissolved in water.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  9. #19

    Join Date
    Jul 2010
    Location
    Southern USA
    Shooter
    Multi Format
    Posts
    3,844
    Kodak D-25 developer was developed as a safer substitute for ppd developers. It is D-23 with the addition of 15.0 g/l of sodium bisulfite. It is said to produce fine grain comparable to that of the phenylenediamine developers with less chance of causing allergic dermatitis.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  10. #20

    Join Date
    Jul 2010
    Location
    Southern USA
    Shooter
    Multi Format
    Posts
    3,844
    Quote Originally Posted by Rudeofus View Post
    I remember I read about some biology book where the average length of some kind of bird was specified as 30.48cm. In the same way I would guess that nobody measured the volume of Sulfuric Acid to four digits (and I'm not entirely sure how exactly one would do this anyway), but that instead some simple number was converted to a different system of measurements. Looking at the other rather odd amounts in the recipe would also suggest this theory.
    There was a contributor to the BJ by the name Cyril Peckham. His formulas were rather curious in that he mixed metric units with English units (grains, scruples, etc) in the same formula. He would use whatever measure gave him a round number. His Amidol paper developer was said to be quite good.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

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