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  1. #41
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    I have found both good and bad information in the work of Knoppow, just as you will find errors in mine.

    Humic acid is not a 'classic' pigment. Cadmium yellow and red lead are pigments, etc. etc. Humic Acid is what I would term a dye. And, this gets back to my basic question. All dyes fade with time, but most pigments do not. Therefore the humic acid dye may fade. Since no one has done a stability test on it, IDK what the answer is.

    PE

  2. #42
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    Both Ammonium Thiosulfate and Sodium Thiosulfate fix silver halide, and both will bleach a silver image if the film or paper is left in the solution long enough. They will both bleach on the acid or alkaline side, but on the acid side the bleach reaction is much faster.

    PE

  3. #43

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    Quote Originally Posted by gainer View Post
    If the dye faded evenly, ...
    it could be restored ... in a
    staining developer.
    Dye then Stain. How about Tan? Tanned gelatin
    of one hue or another. Tanning developers. There
    is no stain or dye involved. A fine point perhaps
    but removes the ambiguity. Dan

  4. #44

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    Quote Originally Posted by dancqu View Post
    Dye then Stain. How about Tan? Tanned gelatin
    of one hue or another. Tanning developers. There
    is no stain or dye involved. A fine point perhaps
    but removes the ambiguity. Dan
    Tanning developers typically produce colored image stain that is proportional in density to the amount of exposure received. So, you end up with a silver image, a stain image and tanned (hardened) gelatin in the exposed areas of the emulsion. Stain and/or dye may both be involved, depending on the emusion design.

    See Haist vol. 1, pages 519-521.

    Pyrogallol and Catechol based developers can provide good examples of staining and tanning phenomena with many different emusions.
    Last edited by Tom Hoskinson; 01-07-2008 at 06:18 PM. Click to view previous post history. Reason: typo
    Tom Hoskinson
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  5. #45

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    Quote Originally Posted by Tom Hoskinson View Post
    Tanning developers typically produce colored image stain ...
    Redundant. Similar to 'from whence' when 'whence' says it
    all. Not exactly Redundant as the gelatine when tanned
    has a color. No dye or stain needed. At least that's my
    understanding. I suppose the color of the gelatine
    varies according to the tanning agent and
    conditions under which it is used. Dan

  6. #46

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    Quote Originally Posted by dancqu View Post
    Redundant. Similar to 'from whence' when 'whence' says it
    all. Not exactly Redundant as the gelatine when tanned
    has a color. No dye or stain needed. At least that's my
    understanding. I suppose the color of the gelatine
    varies according to the tanning agent and
    conditions under which it is used. Dan
    Not redundant - there can be several different things going on. Tanned gelatin may or may not have color, tanning does produce a persistant hardened gelatin relief image. Bleaching the film and redeveloping it can provide a lot of insight.

    The following is an example of redundancy: See Grant Haist, Vol. 1, pages 507 thru 521.
    Tom Hoskinson
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  7. #47
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    Matrix film developer contains pyrogallol. So, it is possible to get both staining and tanning take place at the same time. In fact, the tanning effect could be used to improve sharpness by having imagewise swell effects change the surface of the film much as is seen in Kodachrome.

    PE

  8. #48

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    PE has an interesting idea there. I have seen some old negatives that had that relief effect with the pyro stain. As far as I know, matrix film developer was Kodak D-175 or something similar:

    Kodak D-175 Tanning Developer

    Solution A

    Pyrogallol 4 g
    Sodium sulfite, anh. 5 g
    WTM 1 l

    Solution B

    Sodium carbonate, anh. 25 g
    WTM 1 l

    Mix A and B just before use. Develop 5 to 8 minutes.

    Notice that this has a fair amount of sulfite (2.5 g/l). Stain and tanning are at least somewhat independent. But the old dye transfer books warn you about the limited life of mixed matrix film developer.

    The reasons given in most texts for using an acid fixer are to finish the work of the stop bath to ensure the development is ended predictably and to prevent stains. It really does help prevent those curious and unpleasant splotches that happen when the careless worker carries developer over into the fixer. But it may inhibit some of the staining from pyro developers. I haven't seen any good quantitative work on that subject. My favorite fixer is Kodak F-34, and old color formula that works just fine with black and white film and paper. It's barely acid (pH 6.5). I've used it with Pyrocat HD, and I haven't noticed any effect on the stain, but Pyrocat has relatively light staining in any case. I use fixer as a one-shot for film, and I dump the print fixer after one or two sessions, so life and contamination are not big issues for me.

  9. #49
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    I've used staining devs for the last 13 years, usually fixed in Hypam/IRF-seems to have no visible effect on the amount of stain present [an alkaline fix doersn't seem to make any visible difference IME].So I'm sticking with Ilford/Fotospeed for film as they're readily available , though I might use an alkali fix with FB paper.
    "He took to writing poetry and visiting the elves: and though many shook their heads and touched their foreheads and said 'Poor old Baggins!' and though few believed any of his tales, he remained very happy till the end of his days, and those were extraordinarily long "- JRR Tolkien, ' The Hobbit '.

  10. #50

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    "Modern photographic emulsions designed for tanning development may contain one other compound: the tanning agent itself."

    Grant Haist, Modern Photographic
    Processing, Vol 1, page 520.
    Tom Hoskinson
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