From: robert (robert@RobertSchaller.net)
Date: 01/13/02-09:02:54 PM Z
on 1/12/02 10:56 PM, Judy Seigel at jseigel@panix.com wrote:
>
>
> On Sat, 12 Jan 2002, robert wrote:
>
>> on 1/12/02 9:42 AM, BobWicks@aol.com at BobWicks@aol.com wrote:
>>
>>> Dave:
>>> Diazo salts is the most recent application to replace bichromate that I have
>>> heard of. I do think the light sensitivity is slower. It is currently
>>> being
>>> used in the silk screen industry and it reacts in the same manner that
>>> bichromates do on amino acid chains. As you may know bichromated salts make
>
> You may be mixing apples & bananas here... The diazo used for silk screen
> is (I would assume) used for making the screen, not the final image, which
> would be some kind of ink. It's my understanding that the diazo fades...
> or at least the early books said that. I would also take the fact that
> there's no entry for diazo in Chris James's *very* comprehensive book as
> due to some reason besides ignorance. Diazo is I believe used as a direct
> printing process, for commercial use where archival isn't an issue, but
> not in silk screen.
>
> All that remains in the gum print is pigment & hardened gum arabic, said
> to be as archival as the paper, as platinum, even, assuming the pigments
> are archival.
>
> Judy
There are some interesting points coming out here, and I am very interested
to know how they all add up. Bob Wicks' claim that (as I understand it)
Diazo can be used to photolytically cross-link gum in a similar same manner
to the way in which dichromate cross-links gum is extremely intriguing,
indeed, it would be the foundation of a new process, the gum-diazo print.
Katherine Thayer's observation that
> It is chains of complex polysaccharides, not amino acids, which
> crosslink to harden, or insolubleize, the colloid.
certainly accords well with the observation that gum arabic is mostly
carbohydrate and very little protien -- I've never heard a gum suggested as
a nutritional protien source, whereas albumin (egg-white), casein, and even
gelatin are.
My general question here is, what are these photo-cross linking mechanisms?
Are they described anywhere, say, in the way that Michael Ware explains
Cyanotype chemistry in his book (is this already out of print?)? Such a
thorough explanation would be extremely helpful, and would be of great
sevice in addressing questions like Katherine's:
>Clarification:
>I was speaking here of gum rather than of colloids in general, since the
>discussion had been about gum printing. I don't know much about the
>makeup of other colloids but it certainly seems possible from a
>theoretical standpoint that amino acids could be involved in the
>crosslinking in processes involving gelatin, casein, and albumen. And
>maybe that's the key to the questions we've struggled with before, about
>differences between gum and other processes. Just a thought...
>Katharine Thayer
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