Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,556   Posts: 1,573,158   Online: 773
      
Page 3 of 15 FirstFirst 12345678913 ... LastLast
Results 21 to 30 of 148
  1. #21
    Vaughn's Avatar
    Join Date
    Dec 2006
    Location
    Humboldt Co.
    Shooter
    8x10 Format
    Posts
    4,735
    Images
    40
    Quote Originally Posted by holmburgers View Post
    I've had some glop in my fridge for many, many months now and it doesn't stink or have mold. But, my fridge might be coler than Vaughn's, IDK...
    I take no precautions regarding sanitizing my glassware, etc, I live in a place of constant high humidity, and work in a place that has a constant influx of people walking in and out (mold spores clinging onto air-born dust particles). Plus I refridgerated the glop after it already had been in a hot water bath for several hours. Probably the worse-case scenerio for working with such a great mold-growing medium of gelatin with a bunch of sugar in it!

    And it was the Art Department's fridge -- the secretary called me and asked if the jar of black stuff was possible mine -- it was stinking up the fridge!
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  2. #22
    Vlad Soare's Avatar
    Join Date
    Jan 2009
    Location
    Bucharest, Romania
    Shooter
    8x10 Format
    Posts
    251
    Update:
    I left the glop in warm water for three hours, with occasional agitation on the magnetic stirrer. In the end there were just a few bubbles at the surface, which were removed with a teaspoon. So this time the tissue was perfect and dried with a smooth shiny surface, free from visible defects.
    So far, so good.

    I sensitized it with 3% potassium dichromate for three minutes and exposed it for twenty minutes. However, because I used a "normal" negative (that is, one developed for silver printing, which gives a straight print on grade 3), the 3% solution proved to be too strong. The exposure was also too long. What remained of the final image was too dark and very low in contrast. I'm saying "what remained of the image" because even after more than five minutes in hot water no gelatin came from underneath the tissue, so in the end I lost my patience and peeled the tissue forcefully. A little less than half of the image remained on the paper and continued to develop. I knew I shouldn't use force to peel the tissue from the paper, but by that time it was obvious that something was amiss and the print was going to be ruined anyway.

    I guess the tissue was so strongly overexposed that the gelatin hardened all the way to the support. Am I right?
    It's clear that the concentration of dichromate is too high for my negative. That's why I think that next time I should try a weaker sensitizer, while keeping the exposure time unchanged. Weaker sensitizer means lower sensitivity, so I guess I'd better not shorten the exposure yet. Does this sound like a good strategy?

  3. #23
    paul_c5x4's Avatar
    Join Date
    Apr 2009
    Location
    Ye Olde England
    Shooter
    Large Format
    Posts
    1,542
    Images
    24
    Using a negative that printed fine on grade 2 paper, after doing some test strips, arrived at a three minute exposure on a tissue that had been soaked in 2% potassium dichromate for three minutes. Anther neg I've been working with, I dropped the dichromate down to a 1% solution, soaked for five minutes and exposed for six minutes - Contrast isn't quite where I want it yet, so I'm going to try a 0.75% dichromate next.

    A 3% dichromate solution sounds way to high in my limited experience, so I'd suggest 1% or less (maybe even 0.5%) and do a test strip.

  4. #24
    Vaughn's Avatar
    Join Date
    Dec 2006
    Location
    Humboldt Co.
    Shooter
    8x10 Format
    Posts
    4,735
    Images
    40
    Vald, what light source are you using and for how long?

    It seems to me that if the tissue gets too hot during the exposure, I have problems getting the unexposed gelatin to melt. I have not tested this further, but too much heat does seem to cause some problems the few times I have come across it -- exposing in the sun, for example.
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  5. #25
    Vlad Soare's Avatar
    Join Date
    Jan 2009
    Location
    Bucharest, Romania
    Shooter
    8x10 Format
    Posts
    251
    It's a fluorescent facial tanning lamp. It doesn't seem to give too much heat. Although the body of the lamp itself does indeed heat up, I never noticed the contact printing frame or anything else in the darkroom to be warm to the touch after the exposure. The exposure was twenty minutes, which works well with vandyke prints (though, now that I think of it, vandyke negatives are much more dense, so maybe the time for vandyke wasn't exactly the most appropriate starting point).
    Last edited by Vlad Soare; 02-21-2011 at 11:39 AM. Click to view previous post history.

  6. #26
    holmburgers's Avatar
    Join Date
    Aug 2009
    Location
    Rochester NY (native KS)
    Shooter
    Multi Format
    Posts
    4,423
    Images
    2
    I know there are a lot of variables involved (light source, sensitization technique) and so each person should do his or her own testing.. but, do you think that a reliable method to translate variable-contrast printing grade to sensitization concentration can exist?

    It'd be very convenient to be able to find the desired contrast w/ silver-gelatin and that would leave you with only the exposure time to figure out when switching to carbon.
    If you are the big tree, we are the small axe

  7. #27
    Vaughn's Avatar
    Join Date
    Dec 2006
    Location
    Humboldt Co.
    Shooter
    8x10 Format
    Posts
    4,735
    Images
    40
    Well, if my negative can make any kind of decent silver print, using any paper/filter/developer combo, then I know that I do not have enough contrast for a carbon print (or at least for the way I make them -- YMMD).

    If a negative has too much contrast to make a platinum print with no contrast agent added (Na2, Potassium chlorate, or dichromate), then I know I have a negative that will make a great carbon print.

    I suppose the best way is checking with a densitometer, but I do not have one.
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  8. #28

    Join Date
    Oct 2006
    Location
    Pasadena, CA
    Shooter
    Multi Format
    Posts
    813
    Images
    9
    Quote Originally Posted by Vaughn View Post

    If a negative has too much contrast to make a platinum print with no contrast agent added (Na2, Potassium chlorate, or dichromate), then I know I have a negative that will make a great carbon print.
    Assuming the above, what is your dichromate dilution?

    Oh...and is there a way to determine equal dilutions of either ammonium or potassium dichromates? IOW, a 3% amm di is equal to a ?% pot di solution...

  9. #29
    Vaughn's Avatar
    Join Date
    Dec 2006
    Location
    Humboldt Co.
    Shooter
    8x10 Format
    Posts
    4,735
    Images
    40
    8% AM, diluted 1:3 (one part stock to three parts acetone). For an 8x10 (9x11 tissue) that is 5ml:15ml for brush sensitizing.
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  10. #30
    Vlad Soare's Avatar
    Join Date
    Jan 2009
    Location
    Bucharest, Romania
    Shooter
    8x10 Format
    Posts
    251
    I'm getting close. I used a 1% solution, and the contrast is much better, though there's still room for improvement. I think I'll try 0.75% next time. I used a negative that gives a good straight print on grade 3 paper.
    I think I know what happened last time, when the tissue didn't peel from the final support. The tissue was bigger than the negative, and I didn't mask the edges, so they over-hardened, probably all the way to the support.

    I know there are a lot of variables involved (light source, sensitization technique) and so each person should do his or her own testing.. but, do you think that a reliable method to translate variable-contrast printing grade to sensitization concentration can exist?
    I think it can. I think that if the following things:
    - brand and concentration of gelatin
    - type of pigment and concentration
    - concentration of sensitizer
    - duration of the sensitizing stage
    - sensitizing procedure
    - time between sensitizing and exposure
    - UV lamp used
    - time between exposure and transfer
    are always the same, and both the glop and the sensitizer are made with distilled water, and the sensitizer is always fresh, then a certain concentration of sensitizer should always give the same contrast grade.
    But that's just a guess, based more on common sense than experience. We all know that photographic processes can sometimes elude common sense.

    How long do your tissues take to dry after sensitizing? After two hours mine felt dry to the touch. I gave it one more hour for good measure and then exposed it. It seemed to be completely dry, but after the exposure I had trouble separating the negative from the tissue.
    How long should I wait for the tissue to dry before exposing it? Simple tactile assessment doesn't seem to work.
    Attached Thumbnails Attached Thumbnails carbon1.jpg  

Page 3 of 15 FirstFirst 12345678913 ... LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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