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  1. #11
    Marco B's Avatar
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    Quote Originally Posted by Marco B View Post
    The direct positive process involved exposing silver chloride paper to light, which turned the paper completely black. It was then soaked in potassium iodide before being exposed in a camera. After the exposure, it was washed in a bath of hyposulfite of soda and dried.
    Quote Originally Posted by Igor Savchenko View Post
    From another source http://www.christopherjames-studio.c.../PinholeSm.pdf : “Bayard coated his paper with silver chloride and inserted the moist paper in his camera for a lengthy exposure. Following that, he immersed the darkened print in a bath of potassium iodide to yield a positive image that he fixed in potassium bromide.”
    We now have a serious conflict. One description suggests the potassium iodide bath was done before, and the other after the exposure. A significant difference...

    In addition, the first description suggests the paper was darkened completely before the exposure and bleached during the exposure to reveal the image..., while the second suggests the darkening took place while exposing and the image revealed afterwards?!...

    Anyone else who can elaborate on the direct positive processes Hippolyte applied (both the silver version and/or the cyanotype version) and especially the chemistry going on during the processes?

    Interesting book by the way you referenced Igor (http://www.christopherjames-studio.c...d/thebook.html). I am surprised Christopher's book is not listed on the Alternative Photography website as well... might be a nice addition.

    Ah... well, it is listed, but not on the "Books" main page, but under "Amazone books":
    http://www.alternativephotography.co...k/amazon-books
    Last edited by Marco B; 08-27-2010 at 04:00 AM. Click to view previous post history.
    My website

    "The nineteenth century began by believing that what was reasonable was true, and it wound up by believing that what it saw a photograph of, was true." - William M. Ivins Jr.

    "I don't know, maybe we should disinvent color, and we could just shoot Black & White." - David Burnett in 1978

    "Analog is chemistry + physics, digital is physics + math, which ones did you like most?"

  2. #12
    Marco B's Avatar
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    Well, as usual, even though I was not even searching for this specific Hippolyte Bayard process at all, browsing the internet I hit on the work of Tania Passafiume for the George Eastman House back in 2001...

    Seems she dug into the direct positive process and Bayard quite deeply. Haven't had the time to really go through this 64 page PDF document, but it sure seems interesting enough:

    http://notesonphotographs.eastmanhou...rd_for_web.pdf

    Reading some comments though, it seems quite clear that the potassium iodide was applied before exposure, see the "What is the chemical reaction?" section on page 7.

    Tannia also shows some detailed instructions for re-creating the process.

    I think some of you that seem to be following my posts here on APUG are going to love this document!

    Marco
    Last edited by Marco B; 09-09-2010 at 07:08 AM. Click to view previous post history.
    My website

    "The nineteenth century began by believing that what was reasonable was true, and it wound up by believing that what it saw a photograph of, was true." - William M. Ivins Jr.

    "I don't know, maybe we should disinvent color, and we could just shoot Black & White." - David Burnett in 1978

    "Analog is chemistry + physics, digital is physics + math, which ones did you like most?"

  3. #13
    michaelbsc's Avatar
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    How did you know I was following this?
    Michael Batchelor
    Industrial Informatics, Inc.
    www.industrialinformatics.com

    The camera catches light. The photographer catches life.

  4. #14

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    Quote Originally Posted by mabman View Post
    I find this interesting - can you elaborate a bit on your process? Are you rinsing/wetting the paper before putting it in fixer?
    hi mabman

    what i did was just take a long exposure through a camera ..
    my box camera has a time-setting, so i opened the shutter
    and left it for about 1/2 hour-40 mins ..
    the negatives ( or positives if i contact print a negative this way )
    are kind of delicate. the ones i fixed were in a water bath first
    then partially exhausted speed fixer and the images bleached quite badly.
    i have a recipe for a weak hypo bath for sun prints someone gave me
    that i will use next. i haven't had time to make more exposures to test
    the hypo ...

  5. #15

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    Quote Originally Posted by Marco B View Post
    Well, as usual, even though I was not even searching for this specific Hippolyte Bayard process at all, browsing the internet I hit on the work of Tania Passafiume for the George Eastman House back in 2001...

    Seems she dug into the direct positive process and Bayard quite deeply. Haven't had the time to really go through this 64 page PDF document, but it sure seems interesting enough:

    http://notesonphotographs.eastmanhou...rd_for_web.pdf

    Reading some comments though, it seems quite clear that the potassium iodide was applied before exposure, see the "What is the chemical reaction?" section on page 7.

    Tannia also shows some detailed instructions for re-creating the process.

    I think some of you that seem to be following my posts here on APUG are going to love this document!

    Marco
    hi marco,

    thanks for this nugget !
    it was a great thing to read about
    (and maybe do? )
    john

  6. #16

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    IIRC, the H&D curve for certain emulsions eventually flattens out and then reverses direction with increased exposure. In this latter region density actually decreases with increased exposure.
    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

  7. #17

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    hi jerry

    if the paper was not pre-exposed black prior to exposure ..
    but still coated with the iodide, do you think it would it be a faint negative image,
    ... like an ambrotype?

    i'm relatively clueless
    but ... it seems that what bayard did was make a reversed+fixed version of nicéphore niépce's
    unfixable - lumen / retina prints.

  8. #18
    Photo Engineer's Avatar
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    Jerry;

    You are correct. All emulsions today are treated in some way to emphasize or repress one of those images, neg or pos.

    PE

  9. #19
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    Hippolyte Bayard was not the only one to experiment with a direct positive process, particularly after the advent of the Daguerreotype. Fox Talbot thought that this may be the way to go, thus not realising at the time the full advantage of his own replication process. I would suggest from my own research in this area, that fogging with the first halogen was followed by expose with a second. This is a very interesting area for practical research and one which promises many possibilities for new forms of chemical imagery.

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  10. #20

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    Quote Originally Posted by jnanian View Post
    i'm relatively clueless
    As am I. It has been decades since I have read anything on the subject. The illustration of the H&D curve sticks out in my memory but little else.
    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

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