LF film developers for low SBR

Discussion in 'B&W: Film, Paper, Chemistry' started by Ole, Dec 28, 2004.

  1. Ole

    Ole Moderator Staff Member Moderator

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    You've just dicovered why "non-solvent developers" are also called "surface developers". In this age of time and temperature it's easy to forget that all of the really basic research was done on development by inspection. And these developers really do develop the surface first, and only extreme highlights should be visible through the base.

    I learned it that way, too :wink:
     
  2. Ole

    Ole Moderator Staff Member Moderator

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    At a guess, one teaspoon. The volume won't change appreciably by exchanging Sodium for Hydrogen, evem if the weight changes. Now of you'd weighed the chemicals, it would be a lot more complicated to guess :smile:

    BTW, Amidol would only develop from the bottom in an acidic developer. In neutral to alkaline, it would develop more or less evenly all the way through.
     
  3. gainer

    gainer Subscriber

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    ! teaspoon of ascorbic acid + 1/2 teaspoon of baking soda makes about 4.5 grams of sodium ascorbate. Ascorbic acid ordinarilly uses only 1 hydrogen atom in its acid role. Two atoms are available for reduction of various things such as silver halides. O2 in solution converts ascorbic acid to dehydroascorbic acid and water.

    By weight, 1.91 grams baking soda + 4 grams ascorbic acid = 4.5 grams sodium ascorbate. The same proportions apply to erythorbic acid and sodium bicarbonate.
     
  4. gainer

    gainer Subscriber

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    There is another definition of surface development. It defines the development of the surface of each crystal. The high sulfite developers are supposed to break the surface barrier of a crystal, allowing the developing agent to get at the interior. Most of the early developers contained fair amounts of sulfite. The pyro developers used by H&D had 30 grams per liter. Zawadski describes Xtol as a surface developer because of the isoascorbate (AKA erythorbate) agent, even though it contains probably 80 or so grams per liter of sulfite.