Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 68,750   Posts: 1,483,837   Online: 1107
      
Page 3 of 8 FirstFirst 12345678 LastLast
Results 21 to 30 of 77
  1. #21
    RalphLambrecht's Avatar
    Join Date
    Sep 2003
    Location
    the villages .centralflorida,USA and Germany
    Shooter
    Multi Format
    Posts
    6,151
    Images
    1
    just imaginhow hard and costly itwill be to get all this knowledge and technology back once it is gone. the effort of reentry into a 'lost' technology is gigsntic. 'too bad' just doesn't cut it anymore.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  2. #22
    Rafal Lukawiecki's Avatar
    Join Date
    Feb 2006
    Location
    Co. Wicklow, Ireland
    Shooter
    Multi Format
    Posts
    723
    Quote Originally Posted by RalphLambrecht View Post
    just imaginhow hard and costly itwill be to get all this knowledge and technology back once it is gone. the effort of reentry into a 'lost' technology is gigsntic. 'too bad' just doesn't cut it anymore.
    That's the gist of what I heard Neil Armstrong say about the technology and the know-how of going to the Moon. He remarked, a few years ago only, that we have lost that ability.

    Preserving knowledge, especially that which is unwritten, or is passed on as experience, or remains locked up in corporate drawers to be forgotten lest be shared, seems much more important than society cares for. Many thanks to Ron, and others, for sharing it, and the Ralphs of this world for neatly tabulating it in hugely informative books. Hats off to you.
    Rafal Lukawiecki
    See rafal.net | Read rafal.net/articles

  3. #23
    kb3lms's Avatar
    Join Date
    Jun 2006
    Location
    Reading, PA USA
    Shooter
    35mm
    Posts
    626
    Images
    4
    Ah... so that was a method of "employee discipline" at EK?
    As an aside, there is an electrical engineer that I know that once worked at an Australian colliery on a belt system that moves 24 tons of coal per minute. There was a bug in the software that caused one section of belt to stop dead while the previous section kept running. Due to the mass of the coal it takes the belt a while to stop.

    The miners handed the engineer a shovel and went home.
    All this has happened before, and all this will happen again.

  4. #24
    kb3lms's Avatar
    Join Date
    Jun 2006
    Location
    Reading, PA USA
    Shooter
    35mm
    Posts
    626
    Images
    4
    Ron, this is very interesting. Thank you for your posting.

    We once exchanged some messages about using Ammonium Thiocyanate as a solvent in a double run emusion. I had found it in a Kodak patent from 1967. Is that method used at all for production purposes?

    -- Jason
    All this has happened before, and all this will happen again.

  5. #25
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,722
    Images
    65
    Jason, NH4SCN is used as both a solvent and as a source of Sulfur in sensitization. It rather depends on level and time of addition to get the desired effect. The problem is that SCN is hard to shut off if used as a solvent and so you can over Digest the emulsion leading to fog.

    In some cases, it is (or was) removed by Ultrafiltration which is rather messy for home darkrooms.

    PE

  6. #26
    kb3lms's Avatar
    Join Date
    Jun 2006
    Location
    Reading, PA USA
    Shooter
    35mm
    Posts
    626
    Images
    4
    So, a door is opened to a new mystery. Good!

    Time to check understanding:

    Everything I have made so far has used a full ammonia digest, meaning all the silver has been converted with ammonia before precipitation. (Precipitation being the combining of the silver with the halide to create, for example, silver bromide.) But from my reading and studying, it seems ammonia digest is NOT the way forward to "better" emulsions. (In my case better means more speed with good contrast. I can get to ISO 50, but I want to get ISO 100 give or take a few "isos".) Everything written so far in all these postings seems to confirm that.

    What I gather, then, from this and other postings and books is that a solvent is not actually necessary. And many, or most, emulsions are made without a solvent.

    Ammonia can be used to "homogenize" the crystal types and get you a good (better?) but not ideal dispersion. (Dispersion in this case meaning distribution of sizes and crystal types) The longer the solvent is active, the narrower the range of sizes you get (because the ammonia dissolved the smaller ones and they attach to or form larger crystals) which makes the emulsion more monodisperse, which increases contrast. And you might get a speed increase because you get larger crystals. If you keep this going long enough you get fog.

    But the crystals all become rounded and eventually you wind up with round pebble grains, or klunkers I think you once called them PE. So you would lose any advantage of making cubes, octahedra or t-grains because the ammonia solvent would round them all down to pebbles. So, basically, using ammonia you lose the possibility of controlling crystal habit.

    To summarize, an ammonia solvent makes it easier to get a decently working emulsion but not something you'd actually use in production work. It's a short-cut, but you give up control to get there.

    Am I on the right track?
    All this has happened before, and all this will happen again.

  7. #27
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,722
    Images
    65
    Jason, a true Ammonia digest had been used for years in making high speed (ISO 100 or thereabouts) emulsions but that is not done currently. The reasons are fog, non-uniformity from batch to batch and the odor. Today, the same (or similar) results are obtained with double run emulsions.

    Now, while DR is important, don't dismiss the Ammonia digest. It will work for you and at less cost (but more odor). The only Ammonia make that I don't use and don't recommend is one using NH4X (Ammonium Halide salts) as they have many additional problems and do not work as well.

    I will say that the straight lines and long curves of modern high speed films are obtained by DR makes with vAg control, but then again, a lot of speed comes from the Sulfur+Gold sensitization as well. Without that latter step, you have nothing much.

    PE

  8. #28
    Hexavalent's Avatar
    Join Date
    Nov 2009
    Location
    Ottawa, Ontario, Canada
    Shooter
    Multi Format
    Posts
    528
    Blog Entries
    3
    Several patents refer to the use of thioethers (some being rather exotic crown structures) as "modifying the crystal habit" or "facilitating crystal growth". Would these be considered "solvents" of a type, or something more akin to "catalysts".

    Just for fun, I looked up the pricing on a couple crown ethers and they are mighty pricey little beasts!
    - Ian

  9. #29
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,722
    Images
    65
    Ian, they are very expensive and once present, hard to turn off. They also cause a lot of fog if not handled properly. They are removed by diafiltration after they have done their work.

    PE

  10. #30
    dwross's Avatar
    Join Date
    Feb 2004
    Location
    Oregon Coast
    Shooter
    Multi Format
    Posts
    787
    Quote Originally Posted by Photo Engineer View Post
    The only Ammonia make that I don't use and don't recommend is one using NH4X (Ammonium Halide salts) as they have many additional problems and do not work as well.

    PE

    Must resist posting...
    Must resist posting..
    Dang. Failed.

    http://www.thelightfarm.com/Map/Inde...teHomemade.htm

    http://thelightfarm.com/cgi-bin/html...tent=15Jun2013
    http://thelightfarm.com/cgi-bin/html...tent=31Aug2013
    http://thelightfarm.com/cgi-bin/html...tent=02Sep2013
    http://thelightfarm.com/cgi-bin/html...tent=07Sep2013
    www.thelightfarm.com
    Dedicated to Handmade Silver Gelatin Paper, Film, and Dry Plates.

Page 3 of 8 FirstFirst 12345678 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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