July 2005 Alt-Photo-Process-L: Re: APIS, hydroquinone hardening

From: Katharine Thayer ^lt;kthayer@pacifier.com>
Date: 07/15/05-06:22:12 AM Z
Message-id: <42D7AA6E.E52@pacifier.com>

MARTINM wrote:
>
> ----- Original Message -----
> From: "Ryuji Suzuki" <rs@silvergrain.org>
> To: <alt-photo-process-l@sask.usask.ca>
> Sent: Friday, July 15, 2005 9:38 AM
> Subject: Re: APIS, hydroquinone hardening
>
> > I don't think crosslinking mechanism of chromium is disputed.
>
> Nor do I. But explaining what's actually taking place in detail is pretty
> controversial (to say the least).

Yes, I would say that while the basic idea of photoreduction of chromium
and resultant crosslinking of colloid is well understood in general, and
the mechanism of the reduction of the chromium is fairly well worked
out, the mechanism of the crosslinking itself is not at all well
understood. It seems that every research report that sets out a specific
mechanism for the crosslinking proposes a different model.

The chemist I have been working with was getting preliminary
results that seemed to suggest a different model altogether than any of
those heretofore proposed, but he had to go off and do his real work and
I haven't heard from him since December. But how he got involved with it
in the first place was that I asked him, as a great favor, to read the
literature and tell me how the crosslinking works, since it wasn't at
all clear to me and I wanted to understand it once and for all so I
could finally finish my web page on the chemistry of the gum process.
But after reading the literature, he wrote back to say that there didn't
seem to be any agreement about the mechanism of the crosslinking, and he
found the question interesting enough that he would be willing to put
some time on it himself. His preliminary results, as I said, suggested a
model different from any of the proposed models currently in existence.
I wouldn't go into any more detail than that without his permission; my
point here is simply to echo Martin's contention that the crosslinking
mechanism isn't as straightforward or well understood as is being
suggested here.
Katharine Thayer
Received on Fri Jul 15 13:17:53 2005