Re: Gum problem(s)

On Nov 19, 2005, at 9:13 AM, Sandy King wrote:

> Yves,
>
> There was quite a bit of scientific literature done on dichromate
> colloid systems in the period from 1900-1960. One of the standard
> reference texts on this subject is Light-Sensitive Systems by Jaromir
> Kosar, specifically Chapter 2 on Dichromated Colloids.

"One of the" suggests that there are other standard reference texts on
dichromated colloids besides Kosar? If so, references please?

>
> You must read Kosar with the understanding that certain observations
> may no apply equally to all colloid processes, which has lead many
> to suggest that the book is full of errors. On the whole I think
> anyone interested in any of the dichromate based processes would find
> Kosar interesting, and perhaps useful.

Yves,
I don't know who the "many" are who say that Kosar is full of errors; I
only know of one. . As I leaf through my own copy, I only find my
handscribble "Wrong!" in one place, where he says "The idea that the
dichromate ion might act as a photosensitizer was first proposed by
Galinsky on the grounds of observations made by Brintzinger and Maurer"
and my objection was simply to the citation, not to the information
that the dichromate ion might act as a photosensitizer. And the
objection is miniscule against the information contained in the
chapter. I certainly agree with Sandy that "anyone interested in
dichromate based processes would find Kosar interesting, and perhaps
useful."

When you're done, you still won't know how the gum process works,
because much of what (little) is now understood about the crosslinking
has been learned since this book was published, but you'll have a lot
of subinformation about how dichromated processes work, at least as
applied to dichromated gelatin. The graph I mentioned to you, showing
the relationship between humidity and exposure time in dichromated
gelatin, is in that chapter, on page 81. As I said, there is a similar
graph for dichromated gum arabic that I got from another source, that I
haven't dug out of the pile yet. In this case at least, dichromated
gelatin and dichromated gum seem to behave similarly.

When I first naively asked about the chemistry of the process on this
list, assuming that there was a simple answer to the question, someone
gave the Kosar reference, and someone else chimed back immediately and
said I wouldn't find it useful, but when I found that Powells had a
used copy, I got in the car and drove 3 hours, bought the book and read
the chapter sitting on the curb before driving home again. It was worth
it. Cheers,
Katharine
Received on Sat Nov 19 12:08:24 2005