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  1. #11
    gainer's Avatar
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    Quote Originally Posted by Kirk Keyes
    All this recent talk about stand developing has inspired me to ask a longstanding question that I've had about this technique - I notice that when making up the developer using a 2 part developer like Pyrocat-HD, practitioners seem to maintain the ratio of the A & B parts fairly close to what is used in the "normal", non-stand application. I often see suggestions for 1+1+200 or 1+1+250, or sometimes like Steve Sherman's View Camera article which mentions 1.5+1+233. All these developer concentrations require relatively long development times.

    So what I'm wondering, is has any one tried dilutions where the B part is at a higher conc than the A part, and still in proportions that are similar to the original formulation (1+1+100 or sometimes 1+2+100)?

    I'm curious to find out what happens when the pH of the developer remains similar to what it is in normal dilutions, or perhaps even higher? Using the developer at a higher pH should help push the kinetic balance of the development process, and this should result in shorter development times. But by keeping the A part limited, it should promote the exhaustion of the developer in the highlights.

    So has anyone tried dilutions like 1+4+200 maybe even 1+6+200?

    Kirk - www.keyesphoto.com
    If you want to make use of pH change to reduce local development rate, consider ascorbate developers, which produce acidic byproducts of development.
    Gadget Gainer

  2. #12
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    Quote Originally Posted by gainer
    If you want to make use of pH change to reduce local development rate, consider ascorbate developers, which produce acidic byproducts of development.
    And don't say anything about lack of stain. I, and even you, Photo Engineer, can produce a stained image from an unstained one by bleaching in a rehalogenating bleach and redeveloping in any staining developer. You can have the color of PMK, or Pyrocat, or even hydroquinone.
    Gadget Gainer

  3. #13
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    Patrick, ALL commonly used developing agents produce acidic byproducts. Even I know that. That is why buffer capacity as well as pH are important factors in most all developers. They all change local pH, not just ascorbic acid.

    I grew up not far from Newcastle Pa, and heard that old expression a lot.

    PE

  4. #14

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    Quote Originally Posted by Photo Engineer
    Tom, I would love to see some data from your microdensitometer...PE
    It's published.

    Let's see yours. Does your microsensitometer run on psi energy from Aldeberan?
    Tom Hoskinson
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    Everything is analog - even digital :D

  5. #15

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    Quote Originally Posted by Photo Engineer
    Sandy, the buffer capacity of a solution can decrease with dilution while the pH can stay the same. This is due to the buffering effect itself. As buffer capacity decreases, the production of hydrogen ion becomes gradually more and more significant in the overall reaction, and begins to have its own effect similar to bromide in edge effects. It does not 'drag' in the classical sense of 'bromide drag' due to the lighter nature of hydrogen ion, but rather it tends to diffuse further in all directions.



    PE
    PE,

    OK, so how do you measure the buffer capacity of a solution, as distinct from mesuring its pH.


    Sandy

  6. #16
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    Sandy, buffer capacity is defined as the resistance of a solution to change in pH by addition of acid or base. For example, water is said to have a buffer capacity of zero, and a drop of acid or base will cause a wide swing in pH.

    A solution of Sodium Carbonate at 1 g/l at pH 10 has low buffer capacity, and a solution of Sodium Carbonate at 100 g/l at pH 10 has very high buffer capacity. Addition of one drop of acid to one will cause less change than one drop of acid to the other. The actual capacity is measured by using the pKa of the buffer in question and the concentration. It is usually derived by titrating the solution with acid or base and plotting pH vs the equivalents of base or acid added. The slope of the graph falls to about zero at the maximum buffer point, and the length of the flat portion of the curve is the indicator of the buffer capacity.


    Mixed salts are better than single salts. Therefore, a solution of Sodium Carbonate and Sodium Bicarbonate is better buffered than just one or the other.

    Sodium Acetate and Acetic Acid make a good buffer pair at pH 4.5 and that is why they are used often together in acid fix solutions. They buffer well up to about 6.5 and are often used that high.

    PE

  7. #17

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    Quote Originally Posted by Photo Engineer
    Sandy, buffer capacity is defined as the resistance of a solution to change in pH by addition of acid or base. For example, water is said to have a buffer capacity of zero, and a drop of acid or base will cause a wide swing in pH.


    PE
    PE,

    OK, but what is the relevance of this, for this discussion, to a developer that when mixed has a given pH, and at the end of devleoment has the same pH.

    Based on one of your previous messages I assume that it has something to do with the pH in border areas of heavy and light densitities where the developer is exhausting more than in the general solution. But if so, specifically how does this relate to a developer that begins with a general solution of around pH 10.9 and maintains that pH throughout the development.


    Sandy
    Last edited by sanking; 08-20-2005 at 08:14 PM. Click to view previous post history.

  8. #18
    gainer's Avatar
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    Quote Originally Posted by Photo Engineer
    Patrick, ALL commonly used developing agents produce acidic byproducts. Even I know that. That is why buffer capacity as well as pH are important factors in most all developers. They all change local pH, not just ascorbic acid.

    I grew up not far from Newcastle Pa, and heard that old expression a lot.

    PE
    Actually, the expression originally referred to Newcastle in the British Isles. I was referring to your lecturing Sandy King about pH.
    Gadget Gainer

  9. #19
    gainer's Avatar
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    Quote Originally Posted by Photo Engineer
    Patrick, ALL commonly used developing agents produce acidic byproducts. Even I know that. That is why buffer capacity as well as pH are important factors in most all developers. They all change local pH, not just ascorbic acid.


    PE
    Not as much as the ascorbates. A product of development by ascorbic acid is the dehydroascorbic acid whiich is more acidic than ascorbic acid, as well as the hydrogen bromide, etc.
    Gadget Gainer

  10. #20
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    Quote Originally Posted by gainer
    Not as much as the ascorbates. A product of development by ascorbic acid is the dehydroascorbic acid whiich is more acidic than ascorbic acid, as well as the hydrogen bromide, etc.
    I am not the only one who holds that the products of development by ascorbic acid are more acidic than those of development by hydroquinone and its brothers. See the article by Ryuji Suzuki at his silvergrain.org website
    about ascorbate developers.

    I quote here a portion:

    "The oxidation products of hydroquinone (ones that are exhausted after developing reaction) is alkaline. This may accelerate development in the area
    surrounding areas of intense development reaction. On the other hand, the
    oxidation products of ascorbates are acids, potentially inhibiting development in areas nearby the site of intense reaction. This means that ascorbates are more desirable when adjacency effect and compensation effect are sought."
    Gadget Gainer

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