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  1. #11
    CMB
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    It seems that Kosar (and myself) are guilty of the same thing - advocating a process/procedure that we had not independently verified. Your findings that DAS does not sufficiently harden gum to hold pigment has been confirmed by fellow APUGer and Gummist Rob Shaffer who has been conducting DAS/Gum tests and reported his findings in the November meeting of the Historic Photo Processes Forum. The good news is that he found that DAS works well with casein and Rob will soon be posting his findings here. I am most interested to learn of the results of your experiments using DAS with synthetic colloids.


    Charles

  2. #12

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    Quote Originally Posted by CMB View Post
    The good news is that he found that DAS works well with casein and Rob will soon be posting his findings here. I am most interested to learn of the results of your experiments using DAS with synthetic colloids.
    Charles
    I found several other patents today that reference to the (indeed) french Kalle patent, but I am still not sure what the original patent says about gum. Anyway for me and Rob it doesn't work apparently. I also tested DAS with casein, and indeed it works. I'll post my findings with the synthetic collo´ds (PVA, PVP) soon. At this moment I find exposure times in the range of 15 seconds (!) with one collo´d/DAS mix. Tonal scale is rather short. Synthetic colloids come in various grades, each with their own specifications. Molecule length, degree of hydrolization etc. That makes it difficult to understand all variables. I have been looking through piles of patents with references to aromatic azides, DAS and collo´ds. Very interesting. Kosars' book is still a great standard though.

    -kees

  3. #13

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    Is this group buy still going on? I saw on the other thread that the drop-dead date is January 27th . . . I'd love to get in on this with 100g or so to play with.

  4. #14

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    Quote Originally Posted by sehrgut View Post
    Is this group buy still going on? I saw on the other thread that the drop-dead date is January 27th . . . I'd love to get in on this with 100g or so to play with.
    See this post

  5. #15

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    Thanks!

  6. #16

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    Quote Originally Posted by keesbran View Post
    I looked this up in Kosar's Light-Sensitive Systems and found on page 331 of my 1965 copy, in the section about aromatic azides, a reference to a (Fr. ?) patent (886,716/1942) by Kalle A.G.
    In this reference Kosar states that with gum arabic, dichromates can be replaced by DAS. I wasn't able to track this patent yet, but I have the impression Kosar did not check this himself. As far as I know Kalle A.G. was a German company. It was also active in the production of light sensitive papers, mostly for diazotype, which are not the same as aromatic azides. Kosar states in a note (75) that the patent is french, which is somewhat strange for a german company.

    -k

    I just had a look at FR 886,716. Gum is not mentioned there. The colloids listed in that patent are: gelatin, methyl cellulose and PVA/methyl cellulose.

  7. #17

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    Quote Originally Posted by Hologram View Post
    I just had a look at FR 886,716. Gum is not mentioned there. The colloids listed in that patent are: gelatin, methyl cellulose and PVA/methyl cellulose.
    That's what I concluded from all the references too. Did you find it online somewhere?

    -k

  8. #18

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    Quote Originally Posted by keesbran View Post
    That's what I concluded from all the references too. Did you find it online somewhere?

    -k
    Yes, here: http://depatisnet.dpma.de

  9. #19
    Mark Fisher's Avatar
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    I'm sure you folks know this, but I'd feel guilt if I didn't mention it....

    If this stuff is sodium azide, it isn't exactly harmless....it is highly toxic and dangerous. We use it at work and it is really nasty stuff. Most azides, I believe, are pretty nasty. I'm sure it can be handled safely, but spend some time looking up the precautions.
    Your first 10,000 pictures are the worst - HCB

    www.markjamesfisher.com

  10. #20

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    Quote Originally Posted by Mark Fisher View Post
    I'm sure you folks know this, but I'd feel guilt if I didn't mention it....

    If this stuff is sodium azide, it isn't exactly harmless....it is highly toxic and dangerous.
    It is not. We are talking about: 4,4'-DIAZIDOSTILBENE-2,2'-DISULFONIC ACID DISODIUM SALT or CAS 2718-90-3, with this molecular formula. It's the same as the 'Hardener #3' used in the Ultrastable pigment papers.

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