Here's an example of Mark Osterman's ability to draw, and illustrate ideas in really simple, elegant ways. This is a flow chart showing the most basic steps of emulsion making; in this case a washed emulsion.
The other day Ron joined us at GEH and he too made his way to the chalkboard and we had an excellent classroom session. We hope to do this once a week, or at least a few times a month, in addition to lab work, coating, processing, etc.
There is one term in this drawing that is perhaps not entirely technically correct; or rather, is not in line with the nomenclature that I've learned from Ron's book; Digestion.
Digestion implies the presence of silver-halide solvents (ammonia) and/or chemical sensitizers (sulfur, gold). [Ron, please correct me if I'm wrong here...]
In the simplest form of an emulsion, the prolonged heating step after precipitation of silver-halide is called ripening. This is the process of redistributing and resolubilizing the AgX grains, which on the average, results in larger grains and in turn, more speed.
If you imagine the state of grains after precipitation, we have a distribution of different sizes; some large and some small. The smaller the grain, the more surface area it has by weight. Thus, these smaller grains will become soluble in the presence of heat to a greater extent than the larger grains, and they will redeposit (on average) on the larger grains. The result is 2 fold; more speed from the formation of larger grains and more contrast, as the distribution of grain sizes becomes narrower (less latitude in effect). The pitfalls of course are fog and the destruction of the gelatin's setting point if too much heat is applied.
"Nearly all the mechanisms in silver-halide emulsion making are surface phenomenon"; Ron's million dollar quote.
And there you have a synopsis of things so far.
Chris left out the fact that he also has one emulsion under his belt (and in Mark's refrigerator) for coating and testing in the near future. It is an AgBrI washed emulsion which is good for plates and lantern slides, and which we hope to adapt for making prints.
We spent about 2 hours going over the lab setup and in the classroom and hope to do it again based on Mark's schedule for our joint work at GEH.
So guys, you soon recreating Ilfochrome? j/k ;)
(semi-) joking aside, it's really inspiring to read about your work and studying process, even if I understand only a fraction of all that is written.
Keep up the good work! :)
Thanks. We hope to.
It would be possible to re-create a sort of Ilfochrome. I coated a variation of it back in 1975 or thereabouts. I have 2 of the hard-to-get ingredients here now, but have not been able to get the third. The fourth is really hard to get but I might manage that too.
Chris is humming right along.
What, no sulfur? :)
Originally Posted by Photo Engineer
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Dihestion and Ripening
Chris is right.
Whoops... I did put that in the wrong place. This should have been labeled Ripening. I didn't actually include digestion in that flow chart because it was just a quick sketch made while I was talking to show the very basics. Probably put digestion there because we were talking about it that day. Dyslexics Untie! :-) Given that speed is not so important to me, (remember that I come from startng out with collodion which is much slower) the emulsions I've made in the past don't include any chemical digestion. That will change.
Given my workshop schedule for the past few years, I've had no time at all to shoot my own work or to conduct any new research here at the museum. Having Chris here with the time to experiment with gelatin technology will make it possible to try a lot of different formulas and see if we can coax some interesting results. He is actually the reason why we included gelatin bromide emulsion making, coating and processng in the 2013 schedule. My plan is that he'll be teaching with Ron and me; we need to pass the teaching baton. His first chore....make several batches of clean working emulsion so that he's comfortable with the process and technique. It's a tall order, but we'll get him up to speed soon enough.
We hope that the culture of making hand made gelatin (and collodion) emulsions will be well established with people like Chris, Denise Ross and others by the time the big wheels of industry finally stop making film. Gelatin emulsion makng however is the least active area of hand made photosensitive materials right now. Lots of work to do.
Excellent. I was taught albumen printing by someone who was taught by Mark Osterman.
I'm sure you will get a lot from it.