Re: Colloid photosensitivity

Katharine Thayer wrote:
>
> Hi All,
 but recently I've come
> across this assertion (in a book about the chemistry of chromium) "Many
> colloids such as albumen and gelatin can be insolubulized by ultraviolet
> light."
>
> I suspect that what they really meant is that colloids can be
> insolubulized by ultraviolet light in the presence of dichromate, and
> they inadvertently omitted the crucial phrase. But just to be sure, I
> spread some pigmented gum on a piece of paper and set it out in direct
> sun for 3 hours and then put it in water, and of course it dissolved
> totally in a few seconds; in other words no insolubulization whatever.
>

Since I sent the above, I have come across three more citations
reporting the observation that colloids, or at least that gelatin, can
be insolubulized using nothing but ultraviolet. I thought, well, with
all these citations, and in scientific literature too, (not just
ramblings by well-meant amateur photo-scientists) so maybe there really
is something to this.

Wouldn't that make hardening your gelatin size easy if true -- just hang
the sized paper out in the sun for a while and there you are! hardened
gelatin!

But today I ran the same experiment with gelatin that I ran the other
day with gum (gelatin spread on paper, dried, set out in direct sun for
3 hours) ran hot water over (since gelatin doesn't dissolve in cold),
and there went the gelatin, just like that. (I colored the gelatin with
powdered pigment so I could tell if it was there or not.) In other
words, no insolubilization whatever, just as with the gum.

THEN, I went back to the citations and traced sources back, and sure
enough, all four citations can be traced back to one source, Brintzinger
and Maurer, 1927. Get out the banner Judy, it's time to march for the
cause --- NO CITATION WITHOUT EXPERIMENTATION! Obviously this is just
one of those things that's been passed on without being tested. If it
were a replicable observation, more than one person would have noticed
it in 150 years, for heavens' sake.
 
Sign me Annoyed in the Northwest,

kt
Received on Thu Apr 29 01:41:07 2004