Hi yourself, Judy. I haven't had time to follow up your serendipitous
reference - in a way it's not surprising, although it's interesting that it
predates Kosar's other citations. I re-read some of the articles I refered
to and now wonder if dye-sensitization would really be worth it - especially
if it just shifts sensitivity slightly into the visible spectrum, and
doesn't increase it. Methylene blue probably wouldn't be too hard to
obtain, but the problems caused by precipitation appear to be considerable.
(You could easily increase the pH to 9 as Kubota recommends by adding 28%
aqueous ammonia, but ammonia is so volatile you'd also have to dry the
dye-sensitized dichromated gelatine or gum in a dessicator with an open
dish of ammonia solution [smelling salts!] and silica gel). Solid methylene
green (as used by Graube) is probably much harder to get. Other dyes derived
from fluorescein (like the erythosine mentioned in the article you've
discovered) may overcome the solubility problems of the more sensitive
thiazines (MB, MG, azure A, etc), but are apparently still far from perfect.
According to Kosar, G.O.'t Hooff's sensitizing technique, which involved
bathing dichromated gelatine in various different dyes (including
erythosine) "did not find wide application, because it was necessary to
expose the plates wet to assure maximum sensitivity increase".
The holographers' interest in dye-sensitization comes out of attempts to
achieve sensitivity peaks corresponding to the wavelengths of particular
lasers. But since the sensitivity of dichromated colloids covers a fairly
broad range and extends into the blue end of the spectrum anyway, as
evidenced by the fact that cold light fluorescents can work for gum, maybe a
cold light enlarging head might work. In terms of wavelength, though perhaps
not in intensity, it may even be better than an incandescent lamp from a
slide projector. If this is the case then it's just a matter of increasing
sensitivity. Mild reducing agents in the development bath sound promising.
Hypo is probably a bit too active, but one of the other chemicals
recommended for this purpose is hydroquinone, which you may already have on
hand. Kosar refers to a German thesis of 1932 which would undoubtedly give
more precise quantities, but an initial soak in hydroquinone or a teaspoon
or two in the wash (sounds like an ad for Drive!) might be worth a try if
you need to salvage an underexposed print, even if it doesn't make gum
prints with the enlarger feasible.
************************
To change the subject entirely, in December last year you posted a message
with details about
Photo Techniques, PO Box 585, Mt. Morris, IL 61054-7686 USA
one year (6 issues) is $18.95, plus $5 outside US. 2 years are $34.95
plus $10 outside US and 3 years $50.95 plus $15.
Payment in US Funds, US Bank only.
Phone is 708/965-0566, FAX is 708/965-7639.
Is this still current and have they got an e-mail address yet? I presume
they'd take international credit cards, if it's safe to send one's personal
minutae thru the electronic ether thusly!
Since Camera & Darkroom seemed to make its way slowly but surely to
Australian newsagents, I was going to wait until after I'd actually seen a
copy before I subscribed, but all they seem to stock is yet another English
clone of the Amateur Photographer also titled Photo Techniques. How's the
American Photo Techniques shaping up? Any alt-photo interest?
Philip
pjackson@nla.gov.au