Rae Adams (rae.adams@gtri.gatech.edu)
Tue, 02 Mar 1999 13:43:32 -0400
Having emulsion formulas isn't really all that useful, other than as a
basis of comparison of what is in various types of emulsions and the ways
of "constructing" some of them--in other words, as a learning experience
and as a starting point only. Emulsion formulas are a whole lot like cake
recipes: what works for one person under one set of parameters (altitude,
oven temperature, type of flour, moisture content of ingredients, quality
of shortening, expertise of the cook, etc) is a disaster for someone else.
If you are going to make an emulsion, you have to determine first, what
your needs are (duh, I know--but, a few of the criteria are speed, spectal
sensitivity, grain distribution, halide percentages, type of halides,
contrast range, and feasibility--if you are working with simple equipment,
don't expect to make an elaborate formula reliabily and repeatably). A more
laborious, although ultimately more practical, approach (wasting silver
nitrates can get very expensive) is a thorough understanding of the
principles and theories of emulsion making. That way, when you make an
emulsion and it doesn't turn out like the book said it will (and believe
me, this is exactly what will happen!), then you'll know how to vary what
the emulsion is composed of, the injection rates, the heating times, etc.
to yield an emulsion that will do the job. For example, suppose that your
emulsion has plenty of contrast and speed but that the midtones are
depressed (no, prozac won't work here). If you physically ripen (cook) the
emulsion more to try to boost the midtones, then the emulsion may become
excessively grainy, and you may well start to have an actual decrease in
contrast because of increasing grain size. On the other hand, different
halides will affect local and global contrast as will grain size. So, you
can either change the halide percentage (usually potassium iodide in a
negative emulsion) or the halide composition (cadmium salts yield
contrastier emulsions than potassium, for example--not that I'm
recommending cadium salts). A small change in the potassium iodide in an
emulsion formula will boost or depress midtone densities.
In addition to the books listed in the previous postings (Thorne Baker,
Carol, Mees, Woodbury), one of the most valuable resources I have found is
Eder's Handbook (in multiple volumes), which came out in various editions.
The one published around the turn of the century (around 1907 or
thereabouts) is a good source for the "home" emulsion maker. Unfortunately,
it's in German. A more modern source is the old standy-by Glafkides (1957
and 1959) editions in English; later and earlier editions in French. It has
errors, which you will find when you make them (also Thorne Baker). The
French edition of Clerc's La Technique Photogaphique (published 1947, 4th
edn)) is also useful. Someone learning emulsion techniques on his/her own
faces two problems as far as the literature available (other than you need
to be trilingual--French, German, English--to take advantage of all the
resources): (1) Modern texts incorporate literally a half century or more
technical information gleaned from many researchers, most of which
information can be quite valuable, such as improved methods of spectral
sensitization, speed sensitization, core-shell theory, and t-grain
emulsions. Some of these techniques can be applied on a small scale. (2)
Small scale is exactly the problem. Many of the more current texts are
directed toward the commercial manufacture of emulsions or theoretical
research/laboratory conditions, and we are talking megabucks equipment and
complicated approaches. Thus, a more practical approach may be for someone
interested in emulsions to read articles on emulsion manufacture (and
theory) from 1950 to the present and then apply the results of this
research to the emulsion formulas and equipment/techniques of earlier in
the century.
Perhaps one of the most important contributions to emulsion-making
literature came out of Germany's defeat in WWII. Since so much of emulsion
making is a carefully guarded industrial secret, the publishing of Agfa's,
Farben's (and others) emulsion formulas and techniques was valuable to
commercial manufacturers (for example, gold sensitization) and the home
emulsion maker. Allied intelligence groups published the information taken
from the film, paper, and chemical manufacturing companies (including
formulas for Brovira, Rodinal--600 litres at a time--Isopan, etc.).
Needless to say, some here unnamed photographic companies made quantum
leaps in their film technology after the war. Anyway, this information is
contained in the B.I.O.S. (British Intelligence Objectives Subcommittee),
F.I.A.T. (Field Intelligence Army Technical), and C.I.O.S. (Combined
Intelligence Objectives Subcommittee) (uh, hope I got all the names
right--I'm getting old and forgetful and am too lazy to get up from the
computer right now) reports. Be aware, however, that much of this material
may currently be protected by patents. Reading, however, is free.
There are a number of other emulsion books and articles which could be
useful, and I will be glad to post to the list if there is sufficient
interest.
>
>Jim Browning has posted his recipes and methods for making dye-transfer
> matrix film, from which you can learn a great deal.
>
Agree that it is certainly a learning experience. This is a classic example
of a relatively "simple" emulsion and may provide the interested reader a
good idea of what all is involved in developing and testing an emulsion.
Actually, making an emulsion is easy; making one that works how you want it
to is another matter.
Rae Adams
P.S. If any list members have a good recipe for an angel food cake that
doesn't hiss at you as it falls after being taken from the oven, please
contact me off list.
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