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  1. #1

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    Diazo-Sensitized Carbon Transfer

    The thing I dislike the most about carbon printing is sensitization. Issues of waste dichromate disposal, waiting for the tissues to dry after sensitization...I find it tedious, especially for a "hobby" printer. In a more production-oriented environment, sensitizing, exposure, mating, development can all be batched or pipelined to some extent, but I'm not there. And I don't have the possibility of storing sensitized tissues in my freezer.

    So I'm intrigued by the possibility of a diazo-sensitized tissue that is stable on the order of weeks (or even more, perhaps), so that I can just make one print (relatively) quickly, when I have a chance. In poking around some dark corners of the internet, I came across an anecdotal report of someone using a screenprinting diazo sensitizer with gelatin. (This was to make dye-transfer matrices, but the principle is the same).

    http://tech.groups.yahoo.com/group/d...er/message/123

    Not being able to track down the specific emulsion the poster wrote about (Nazdar 101), I used one that was available at my local art store, the Speedball emulsion sensitizer, reasoning, as the OP did, that most of the screenprinting emulsions are probably similar.

    Well, I did this, and mixed up a small batch of glop, to which I added the sensitizer. I noticed that the consistency of the glop was different as I was pouring it. A bit thicker, and a little "gummy". Dried for about 44 hours in black or red-safelight conditions.

    The poured tissues were completely insoluble. So something went wrong...now I just have to figure out what.

    I have a couple of thoughts, and I'd be curious what the collected wisdom thought...

    1) The diazo sensitizer used is completely incompatible with gelatin. Not much I can do there except try and find a different option.

    2) The sensitizer I used is not stable enough, and broke down over the 2-day drying period of the tissues, hardening the gelatin.

    3) I added way too much sensitizer. Despite using roughly the same proportions as the message I referenced above, the chemicals were sufficiently different so as to make the amount I added a gross excess, which contributed to the hardening.

    4) Despite the MSDS identifying only the diazo dye and some phosphoric acid (which I assumed would not affect the gelatin in the quantities used), perhaps there was some other substance in the dye solution that caused the hardening.

    5) The high temperature of the glop solution (115 F) caused the sensitizer to break down and harden the gelatin.

    I'd love to explore the possibilities of this more, but I don't know where to go from here. Any help regarding sensitizer sources (or particular commercially-available compounds to look for), methods, etc. would be greatly appreciated.

    --Greg

  2. #2
    CMB
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    The info you are seeking can be found in Kosar, Light Sensitive Systems, Wiley,1965. Although he devotes a whole chapter to Diazotype Processes, you will probably find his discussion of Aromatic Azido Compounds starting on page 330 the most useful. Allow me to quote:

    "In combination with gelatin, glue, gum arabic, etc. aromatic azide compounds were suggested for about the same processes as previously described dichromates…"

    Add to this: non-toxic, no dark reaction, and capable of long term storage after sensitization.

    This is what was/is used as the UltraStable sensitizer.
    Last edited by CMB; 06-20-2011 at 01:31 AM. Click to view previous post history.

  3. #3

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    Thank you, Charles, for the reference. Much as I had been looking for a concise, practical answer, I realize that I know little to nothing about the chemistry at play here (my background is in micro-electronics), and so a little education is definitely in order.

    Turns out Powell's Books here in Portland had a nice, affordable copy on the shelf, just waiting for me. Now I just have to find an excuse to go downtown and pick it up...

    Quote Originally Posted by CMB View Post
    Add to this: non-toxic, no dark reaction, and capable of long term storage after sensitization.
    I always thought the last 2 were intrinsic to this family of compounds. I guess not.


    While you've previously identified the UltraStable sensitizer, I'd also like to find compounds that may be more readily available, and perhaps less expensive ($54 for 10 grams from the one source I was able to find online) than that, though I certainly don't know how far 10g would take me.

    --Greg

  4. #4
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    Greg, it's awesome that you're taking this work upon yourself. Aside from UltraStable, is there anyone out there using diazo sensitizers for carbon?

    I actually corresponded with that fella from the dye-transfer post you linked to (small world!); I'll dig up the email and see if he gave any tips.

    Out of curiousity, what was your tissue support & pigment?

    update: How much sensitizer did you use? The DT-Yahoo! post says 4mL per 100mL, but in our personal corerspondance he says "250ml water, 15 ml gelatine, with sugar (amount appears to depend on humidity), and six drops of speed ball sensitizer". Perhaps you're adding too much?
    Last edited by holmburgers; 06-20-2011 at 12:03 PM. Click to view previous post history.
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  5. #5

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    So my recipe was my standard high-relief tissue, and it was a small batch.

    14g Gelatin
    125 mL Water
    4mL Glycerin
    0.8g M.Graham Lampblack Watercolor
    10mL Isopropyl Alcohol

    I pour onto Dura-Lar clear 0.005" film.

    The OP had said that 4mL for an 8% gel solution was pretty high contrast. Since I'm using more gelatin, and wanted a lower contrast, I used 10mL for that batch. 6 drops is waaaaaayyy different than 10mL (using the old rule of thumb that 20 drops = 1 mL)

    In doing some digging around, I've discovered something. The other manufacturers he mentions (Kiwo, Ulano, Nazdar), all use the same sensitizer, Diphenylamine-4-diazo sulfate CAS # 41432-19-3. So perhaps the 4mL / 100mL (8% gel) is appropriate for these.

    Speedball uses something different: Polymethylene-p-Diazo Benzene Dye CAS #71550-45-3.

    As far as I can tell, Speedball is the only one that is still available separately (without having to buy and then discard the screen emulsion).

    I won't get a chance to try anything else until after the 4th. But if we continue to have a cool summer, I can make some other tests. If it warms up, then it gets too warm for me to pour tissues (no A/C), and it will have to wait 'til fall.

    --Greg

  6. #6
    mdm
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    Looking at MSDS sheets it seems some screen printing sensitisers have formalin in them, which would explain insoluble tissue.

  7. #7
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    But screen printing relies on the use of an emulsion as well, how does it not harden that?

    That's a great lead though.
    If you are the big tree, we are the small axe

  8. #8

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    Quote Originally Posted by mdm View Post
    Looking at MSDS sheets it seems some screen printing sensitisers have formalin in them, which would explain insoluble tissue.
    Yep...I saw those data sheets. That is not the sensitizer I used, so that can't be the exact problem that I had. But I saw one datasheet that listed the chemical in question as:

    Chemical name DiazoniumSalt: p-diazodiphenylamine sulfate, formaldehyde condensate (41432-19-3).
    Note: End product does not contain free formaldehyde.
    Emphasis mine.

    In the thread from the dye transfer list that I linked to, the OP claims to have tested (successfully) a number of different manufacturer's sensitizers, some of which use the chemical above. I plan on testing it if I can get my hands on it (without having to also purchase the screen emulsion along with it.)

    --Greg

  9. #9
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    I was told by a collaborator that in Bob Pace's "Keeping Pace" newsletter there is something about a diazo-sensitized emulsion of Mssr. Berger's that worked well for imbibition.

    I'm gonna try to get a hold of that; Charles, do you happen to have a copy of that easily available?
    If you are the big tree, we are the small axe

  10. #10
    CMB
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    Check out the "Keeping Pace" newsletters from 1994-1996. I had first shown Bob some dye transfer prints made by Girard Aniere in 1994 using UltraStable films (the same ones you have) to form the matrices. Although the enlarged separations were made with a 400lpi screen, the print appears to be continuous tone (even when viewed with a high power magnifier) because of the diffusion of the dyes. I've uncovered some correspondence with Bob in 1996 also discussing this approach to making dye-transfer prints but I can't refer you to any specific issue of his newsletter that covers this topic.

    BTW : Bob Pace, in 1997, published his book Making Enlarged Separation Negatives for the UltraStable Process, which may be of interest to those who wish to use con-tone negatives to produce color carbon prints.

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