silver gelatin starter (Re: Dark reaction in dichromated colloids)

From: Kate Mahoney <kateb@paradise.net.nz>
Subject: RE: Dark reaction in dichromated colloids
Date: Tue, 15 Jun 2004 09:29:31 +1200

> BTW I'm becoming interested in making my own silver emulsion -
> anyone got a good recipe, technical hints?? The only recipe I've got
> is in a 1908 Photographer's dictionary and it looks very very very
> complex - surely there is a "kinder, gentler" way????

Unfortunatelly, there isn't any good single source for emulsion
hobbyists, at least if you try to make enlarging paper emulsions.
There are many old decent plate emulsion formulae published that work
ok if you follow them with a couple of mods, though there are rooms
for improvement (and there's an easier way to do the most time
consuming part).

The reason why enlarging paper emulsions are hard is that most good
published formulae call for cadmium chloride or other cadmium salts.
Depending on how it's added, how much of it is added, and to what
emulsion it is added, its effects differ greatly. And I certainly
don't recommend to have this thing around for health and environmental
reasons. Same for mercury compounds that were used as emulsion
stabilizers for decades. I have one good candidate for its
substitution and I'm working on emulsions using it.

Bromide and iodobromide plate emulsions are simpler as long as you are
happy with rather slow speed, and some old formulae would work ok
today, with a small amount of sulfur sensitizing agent added to make
up for the difference in the kind of gelatin used today. For these,

Carroll, B. H. 1931. The preparation of photographic emulsions. J. of
Chem. Education, 8, 2341-2367.

and

Hill, T. T. 1966. Laboratory-scale photographic emulsion technique,
J. of Chem. Education., 43, 492-498.

would be a good starting material. I have a long list of literature
but they are heavily loaded with physical chemistry and solid state
physics. If anyone with enough background is interested in reasonably
current review articles, there are a few good ones written by retired
scientists from Eastman Kodak, and a whole book by current Fuji
scientist. But they aren't written for average photographers. One
more thing to note.

Reed, M. and Jones, S. 1995. Silver gelatin: a user's guide to liquid
photographic emulsions. London: Argentum. (reprint edition dated 2001)

This is a nice little book with interesting ideas, but the technical
sections are marred with errors and misconceptions. Formulae contain
many errors. Their references section is inaccurate and contain many
non-standard abbreviations that make the list useless. If you think
the first half of the book is worth the price, which I do, it's a good
book to have. But if you plan to write a book on this subject later,
this book is definitely not where you want to cut and paste the
technical issues from. Let's hope new edition will solve this issue...

Indeed, store bought emulsions should be ok for most printing needs
and home made plate emulsions would be of decent quality at least for
pre-1930 standard. It took me several serious attempts to figure out
printing emulsions of high contrast, good Dmax and fog-free crisp
highlights. Printing emulsions are made for much higher contrasts and
unsuitable for in-camera negatives. So these two would be nicely
complementary.

There are a couple of well mentioned emulsion how to books published
from late 20s to late 40s. They contain many errors, misconceptions,
dogmatized superstitions and what not. At least one of them call for
highly toxic chemicals (acute effect is worse than cadmium) as if it
were nothing. I referred to those books before when I didn't know
better. I had to start somewhere like most others, but I can tell you
one thing --- save your time and money and leave those books for
collectors.

--
Ryuji Suzuki
"You have to realize that junk is not the problem in and of itself.
Junk is the symptom, not the problem."
(Bob Dylan 1971; source: No Direction Home by Robert Shelton)