Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 69,727   Posts: 1,515,112   Online: 1153
      
Page 1 of 4 1234 LastLast
Results 1 to 10 of 33
  1. #1

    Join Date
    Jan 2009
    Location
    Fallbrook, California
    Shooter
    35mm RF
    Posts
    23
    Images
    1

    Odd Gum Bichromate Problem

    I ran into a curious Gum problem. I am a new gum printer, so this may seem basic to more experienced folks.

    Recently I switched my sizing formula from hardening with Glyoxal to Glutaraldehyde. My sizing problems were resolved by the change. At the same time, my old supply of gum ran out and I opened a new container (from Photographer's Formulary).

    Suddenly I observed an increase in required exposure of about 3x (1.5 stops).

    Since I changed two variables at the same time I am uncertain about the cause of the sudden increase in required exposure. I doubt it was the change in my sizing formula and I suspect that the change from "old gum" to "new gum" is the culprit.

    Has anyone else experienced this kind of change and does anyone have any idea what may have caused it? I would appreciate any insight.

  2. #2

    Join Date
    Oct 2005
    Location
    Pakistan
    Shooter
    Multi Format
    Posts
    266
    First, just as a matter of interest, allow me to ask how you came about this new formular. I have not heard of Glutaraldehyde as a hardening agent. I have just read in Wikipedia, however, that it has very irritating smells. So, what is the advantage over glyoxal? Could you tell the dilution you use?
    Regarding your question, I would guess otherwise, and suspect the new hardening method as the culprit - even though, given the many variables in direct pigment processes, it is hard to tell.
    Do you add the hardening agent to the gelatine when sizing the paper or do you harden in an extra step? Do you wash the paper after hardening? If not, I suspect there might lie the problem.

  3. #3

    Join Date
    Sep 2005
    Location
    Istanbul, Turkey
    Shooter
    Multi Format
    Posts
    636
    I remember reading somewhere that the acidity of your gum solution affects printing speed e.g. high pH (more alkaline) -> slow speed, low pH (more acid) -> high speed. (AFAIK, this is also observed in carbon printing when using dichromate sensitizers with different pH levels...) So, if everything else was kept constant, I'd suspect that the cause is different pH of new gum and/or different pH of the new hardening solution (affecting the surface pH level after application). But that's just an educated guess -> never experienced something like that!

    Regards,
    Loris.

  4. #4
    Kerik's Avatar
    Join Date
    Nov 2002
    Location
    California
    Shooter
    Medium Format
    Posts
    1,465
    Images
    238
    Glutaraldehyde as a gelatin hardener has been discussed in depth on the alt-process email list. Many people seem to like it, but it didn't work well for me. I prefer Formaldehyde.
    Kerik Kouklis
    Platinum/Gum/Collodion
    www.kerik.com
    2014 Workshop Schedule Online

  5. #5

    Join Date
    Jan 2009
    Location
    Fallbrook, California
    Shooter
    35mm RF
    Posts
    23
    Images
    1
    I was having minor staining problems with Glyoxal so I wound up double coating the gelatin, that lead to coating issues "fisheyes" in the sensitized emulsion. So I gave Glutaraldehyde a try based on Christina Z. Anderson's book. Glutaraldehyde is a cousin of formaldehyde and probably just as toxic, so extra precautions are required. I size in small batches, currently 5 9x12 sheets for 8x10 printing. For that I mix 50 ml. distilled water, 1.3 g. gelatin and 0.3 ml. of 2.5% glutaraldehyde. With this mix the "fisheyes" can be easily eliminated while brushing on the emulsion and single coating works. I would guess all of this relates to the eccentricities of my location and workflow and I think glyoxal is a good hardening agent. It is said that some have an issue with glyoxal yellowing but I have not experienced it. Glutaraldehyde is a newcomer to gum printing but reportedly has a good history as a gelatin hardener for silverprints and is apparently used by those who make their own printing emulsions.

    I mix the hardener into the warm gelatin just prior to coating. I have not washed after hardening and I appreciate the suggestion. If I have more issues I will add a washing step after sizing.

    It could well be the glutaraldehyde that is changing the exposure times. I really don't know. Fortunately is is a managable problem.

    Thanks Again!

    jh

    Quote Originally Posted by Lukas Werth View Post
    First, just as a matter of interest, allow me to ask how you came about this new formular. I have not heard of Glutaraldehyde as a hardening agent. I have just read in Wikipedia, however, that it has very irritating smells. So, what is the advantage over glyoxal? Could you tell the dilution you use?
    Regarding your question, I would guess otherwise, and suspect the new hardening method as the culprit - even though, given the many variables in direct pigment processes, it is hard to tell.
    Do you add the hardening agent to the gelatine when sizing the paper or do you harden in an extra step? Do you wash the paper after hardening? If not, I suspect there might lie the problem.

  6. #6

    Join Date
    Jan 2009
    Location
    Fallbrook, California
    Shooter
    35mm RF
    Posts
    23
    Images
    1
    That is a good guess I think. I may have gotten a big increase in required exposure from both the hardener and the gum contributing to the situation. I was surprised, but I should know by now that gum has its surprises.

    Thanks,

    jh


    Quote Originally Posted by Loris Medici View Post
    I remember reading somewhere that the acidity of your gum solution affects printing speed e.g. high pH (more alkaline) -> slow speed, low pH (more acid) -> high speed. (AFAIK, this is also observed in carbon printing when using dichromate sensitizers with different pH levels...) So, if everything else was kept constant, I'd suspect that the cause is different pH of new gum and/or different pH of the new hardening solution (affecting the surface pH level after application). But that's just an educated guess -> never experienced something like that!

    Regards,
    Loris.

  7. #7

    Join Date
    Jan 2009
    Location
    Fallbrook, California
    Shooter
    35mm RF
    Posts
    23
    Images
    1
    I imagine formaldehyde does just fine as well as repelling any bugs interested in dining on one's prints.

    Thanks,

    jh

    Quote Originally Posted by Kerik View Post
    Glutaraldehyde as a gelatin hardener has been discussed in depth on the alt-process email list. Many people seem to like it, but it didn't work well for me. I prefer Formaldehyde.

  8. #8

    Join Date
    Oct 2005
    Location
    Pakistan
    Shooter
    Multi Format
    Posts
    266
    I think Loris' guess may actually be the right one. I misread your, Jon's, first message - with hardener problems, exposure times should go down, not up, and there shuld be problems with clearing. (on the other hand, casein is very alkaline, as it is dissolved in ammonia, and gives me consistently shorter exposure times than gum).
    I have never experienced "fisheyes", don't even know exactly what this means - bubbles in the dichromate mix?
    Also, I have only ever used glyoxal. Paper does develop an orange stain if it is kept for some time after sizing/hardening, and if it is not washed after the hardening step.
    For this reason, and because sizing mistakes can be corrected, and also because dissolved gelatine may be ket in a fridge, I brush on gelatine first on dry paper, dry, and then apply the glyoxal solution with a foam brush, dry, wash. I find this little extra work, and I don't get orange stains even if I keep the paper. Also, I size full sheets and cut them to size later.

  9. #9

    Join Date
    Sep 2005
    Location
    Istanbul, Turkey
    Shooter
    Multi Format
    Posts
    636
    Lukas, casein (proteins) and gum (polysaccharides) are quite different and may behave pretty differently -> so that would be comparing apples to oranges.
    BTW, I have 2kg's of Kremer Casein that I would like to make use of. What would be your suggestions to me for dissolving the casein? (I have concentrated ammonia; how much casein in how much water and how much ammonia for a neatly working coating solution? How much dichromate; strenght, casein+dichromate ratio?... How do you develop your caseins? Just simple automatic development or by manipulation?)

    Thanks in advance,
    Loris.

    P.S. (Have you had to look for the type/brand of the varnish BTW?)

  10. #10

    Join Date
    Jan 2009
    Location
    Fallbrook, California
    Shooter
    35mm RF
    Posts
    23
    Images
    1
    Hi Lukas, Thanks for the clarification. I will assume the new batch of gum is most likely responsible for the change.

    "Fisheyes" are small areas (2-3mm) where the emulsion draws back creating a hole in the coating. This could be caused by excessive thickness gelatin in the sizing. I usually see it in the red layer of a tricolor, possibly because my red is an earth color and the other two are not.

    jh

Page 1 of 4 1234 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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