Re: Dry Plates

While I understand your motivation, you are trying a difficult
route. Positive emulsions and print emulsions are significantly easier
to master than negative emulsions. I recommend to get started with a
decent bromide paper emulsion and then move on to slow plates.

The bare minimum requirements are:

silver nitrate (high purity, like analytical reagent)
deionized water (high purity)
photographic gelatin (inert, deionized, 200-300 bloom, ossein)
potassium bromide (high purity)
potassium iodide (high purity)
sodium thiosulfate
benzotriazole
a refrigerator (something cold enough to chill set the emulsion in dark)
a good mechanical stirrer
a good heating device to keep the solution at a constant temperature
for 1-2 hours (for nontabular grains, typically 50C)

You can make a slow print emulsion of ISO P100 speed and about grade
2-3 reasonably easily. If you want to improve speed, contrast, Dmax,
silver economy, shelf life, etc., or simplify the making process,
there are a lot of things that can be done but they always require
additional agent and/or processing step.

Forget about panchro. How are you going to make, coat and dry the
emulsion in total darkness? I haven't figured out a way to do so. I am
making blue-sensitive color blind emulsions, green-sensitive ortho
emulsions, and some infrared emulsions. I still need to build a proper
safelight to make practical IR sensitized material.

Then you'll have to think about more realistic goals. In history of
emulsion technology, there were some breakthroughs that improved the
emulsion. You can mix and match those technologies to do what you want
to do. ASA25 emulsion is something I can make in one afternoon easily,
but it was hard at first. You probably want to begin with ASA single
digit as the first goal. Such speed is more realistic for a simple
making process.

In order to exceed ASA 10 range, if you do a classic single jet,
you'll need a good ripener and good sulfur sensitization technique, at
least. ASA single digit range can be made with small unripened
crystals with moderate sulfur sensitization. You can also increase
speed with sulfur-plus-gold sensitization but you'll need a few more
ingredients and good technique to do this right without increasing
fog.

Another thing is that, you have to get good photographic gelatin. Bad
gelatins often give slow speed, fog, or both, and it's not worth the
effort. Purity of other ingredients (including water) also counts.

You might be disappointed to hear all these, but you'll be a lot more
disappointed when you jump on to "ASA25" emulsion that gives you
nothing but fog every time you make it. With slow bromide print
emulsion, you can still make large prints from small negatives without
going to digital negatives or ULF.

If all these don't make you depressed, let me know :-)
Received on 06/22/06-12:20:39 AM Z