Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,934   Posts: 1,585,599   Online: 738
      
Page 13 of 17 FirstFirst ... 37891011121314151617 LastLast
Results 121 to 130 of 166
  1. #121

    Join Date
    Oct 2006
    Shooter
    Medium Format
    Posts
    131
    Quote Originally Posted by wildbillbugman View Post
    Hi,
    Jeff uses difussion to intoduce the silver nitrate into the gelain coating. Unless I am way off, the only way to vary grain sise would be to coat a pre-existing, larger grain silver halide emulsion on the glass, then then spectraly sensitize the coating with dyes + ascorbic acid.
    Do you have a source for the dyes Jeff used ?

    I ment to say "spectraly sensitize by diffusion."

    Yes, with the Diffusion method you can also spectrally sensitize a unsensitized AgX emulsion subsequently. In contrast to former bathing methods, this one uses a halide/dye/ascorbate solution for sensitization. I think it's this combination that does the spectral sensitization more efficiently than previous attempts.

    As for forming larger grains with the Diffusion method, you could well do that by adapting the bath concentration. E.g. increasing the amount of halide most certainly does increase grain size. Similarly, longer bathing periods in the halide bath will equally favor the production of larger grains. Furthermore, you might increase the temperature of these baths and the drying section etc.

  2. #122

    Join Date
    Apr 2005
    Location
    San Bernardino, CA
    Shooter
    8x10 Format
    Posts
    749
    Dear Hologram,
    I wonder, why the lithium bromide and not potasium or ammonium bromide?
    Bill

  3. #123

    Join Date
    Oct 2006
    Shooter
    Medium Format
    Posts
    131
    Quote Originally Posted by wildbillbugman View Post
    Dear Hologram,
    I wonder, why the lithium bromide and not potasium or ammonium bromide?
    Bill
    According to Jeff Blyth lithium bromide does form smaller grains than potassium bromide (I am not sure about ammonium bromide). Furthermore, LiBr has better solubility in alcohols – that may be important when using certain sensitizing dyes.

  4. #124
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    23,558
    Images
    65
    Just a note for y'all.

    Making an emulsion in-situ on a plate or film support yields a very slow emulsion due to the lack of proper solution emulsification steps. So, although it can be done, the results are slow emulsions.

    Spectrally sensitizing them on plates has also been very difficult due to uniformity problems and other technical details. It can be done, but not with the efficiency that is achieved by doing it in the solution of pre-melt.

    For those that have counter arguments, all I can say is that I have access to those who have done the above both ways. This was a summary of their comments.

    PE

  5. #125
    JOSarff's Avatar
    Join Date
    Mar 2008
    Location
    Santa Fe, NM
    Shooter
    8x10 Format
    Posts
    203
    Why is there a problem with purchasing sensitizing dyes? Is there some use that wI don't know about that makes them a 'banned' substance?

    Joe
    There is no such thing as taking too much time, because your soul is in that picture. -Ruth Bernhard

  6. #126
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    23,558
    Images
    65
    Joe;

    They are not banned. The good ones are very difficult to make with a limited market and therefore very expensive. They run about $100+ / gram. Thats about the whole story in a nutshell.

    PE

  7. #127

    Join Date
    Apr 2005
    Location
    San Bernardino, CA
    Shooter
    8x10 Format
    Posts
    749
    The larger companies,specificly Aldrich will sell some dyes
    to anyone. But other specific dyes may be sold only to businesses and institution. Sometimes it is difficult to see the reasoning behind Aldriches classification of these dyes. I have not tried Fisher Scientific, but when I purchased some filter paper from them last week, the invoice had, in big bold letters "DO NOT SHIP CHEMICALS". I do not know if this is common, or if I am on the industral equivalent of a "NO FLY LIST". I am not an Arab, have never been in a Mosque, nor have I ever sent a nasty letter to a public official. In fact, I have had security clearances for some of my jobs. I think that it is "one Rule Fit All".
    Bill

  8. #128
    JOSarff's Avatar
    Join Date
    Mar 2008
    Location
    Santa Fe, NM
    Shooter
    8x10 Format
    Posts
    203
    Quote Originally Posted by wildbillbugman View Post
    I do not know if this is common, or if I am on the industral equivalent of a "NO FLY LIST". I am not an Arab, have never been in a Mosque, nor have I ever sent a nasty letter to a public official. In fact, I have had security clearances for some of my jobs. I think that it is "one Rule Fit All".
    Bill
    Nor am I, but it seems to get harder to get supplies every year. Just a venting.

    Joe
    There is no such thing as taking too much time, because your soul is in that picture. -Ruth Bernhard

  9. #129

    Join Date
    Jun 2004
    Location
    Portland, OR
    Shooter
    4x5 Format
    Posts
    3,268
    Just don't ask about buying iodine or phosphorus - they'll mark you as a meth cook and you'll never be able to buy anything.

  10. #130

    Join Date
    Apr 2005
    Location
    San Bernardino, CA
    Shooter
    8x10 Format
    Posts
    749
    Kirk,
    Anyone who has bought crystaline Iodine from The Formulary has filled out a "DEA card". I don't know who gets these cards, but I have never been"Raided"(yet).
    Bill



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin