As some of you will remember, a while back (geez, 11 years ago, yikes) I took a workshop in making gelatin emulsions. It was the second workshop I took in the historic process workshops then taught at Eastman House (now George Eastman Museum) in Rochester, and the one that really grabbed me. I've been making, coating and shooting them ever since. While I won't say that I've mastered the process, I think it's fair to say that I've reached journeyman status, as last year I got the opportunity to help teach a workshop on the subject and it went very well. But that's another post (that I should have made but didn't. May well do a separate one on that, as it was an interesting experience. And maybe one on all the other processes I ended up learning in about a dozen years of different workshops.)
Anyhow, fast forward to the present. I just got home from a week of serving as a lab assistant while Mark Osterman (retired from Eastman) worked on making some batches of emulsion and working to coat them on film (rather than the glass plates I normally work with). He'd managed to collect an old Polaroid Research DIY film coating machine via RIT and an ex-Kodak perforator, and rigged a setup for slitting the master roll that came off the machine. In it's current configuration, it can only coat 6-7 ft (a couple meters) of film, but that's enough for a 36-exposure roll of 35mm or a standard roll of 120. He was getting ready for a visit from the conservation lab at SUNY Buffalo to do some demonstrations, and it was an opportunity to for me to mess around with the cool toys and help him out as an extra pair of hands and eyes as we went through the process.
For the project, we made two emulsions, the first being "MO-1880", which is a blue/UV-sensitive emulsion that corresponds to what people were making about 1880. It's slow but very clean and fine-grained. As to speed, ISO doesn't really make sense with blue-sensitive, as it's so dependent on the spectrum of light used, but it's probably reasonably close to ISO 2 or 3. Can be a bit faster in good (blue or UV heavy) light, and a lot slower otherwise. Then we take some of that base emulsion and sensitize it further to make it a bit faster. There are different techniques for this available to the DIY maker (that's yet another post) but this time we're going for a fairly simple one of adding a minute amount of sulfur, in the form of a dilute solution of sodium thiosulfate (yes, fixer) that gives it a boost in speed. If you're lucky, you can get to ISO 12 or so in good light, and more is possible with other techniques, at the risk of a bit more fog, and possibly larger grain. The grain is generally a non-issue with plates, being large format, but can be more of a problem for smaller formats. For other projects that I can't talk about yet, Mark is wanting something corresponding to common 35mm film from about 1925, so we're aiming for that, calling the result "RM-1925" (RM for Ron Mowrey, who worked with Mark and Nick Brandreth to formulate some faster emulsions before Ron sadly passed a few years ago).
Once we made the emulsion we wanted to use, we loaded up a film coating machine he'd acquired that is an amazing Rube Goldberg (or Heath Robinson if you're from the UK) kind of thing: made from an old Sears abrasive belt grinder and some custom machined parts at Polaroid Research back in the day, it was donated to Rochester Institute of Technology (RIT), and then to Mark when they stopped using it. It has a coating head made of two pieces of machined stainless steel separated by a plastic shim that sets the gap that the heated emulsion flows through. Then a length of film base is attached to the platen of the old grinder and around the rollers, then clamped down and sliced to make a continuous loop. The emulsion is loaded into a separate machine that consists of a stainless steel syringe driven by an electric motor through some gearing (to allow for multiple speeds) that drives a lead screw attached to the plunger of the syringe. The syringe is connected to the feed head via a flexible tube. Coating requires mounting the film base, splicing it cleanly, getting it centered and running true, positioning the splice just past the coating head, loading the syringe with emulsion heated to the right temperature, then installing it in the pump, connecting the hose, running the pump to start the emulsion flowing (you can see it travel through the tube), then, when it just reaches the coating head, turning on the belt drive on the coating machine and hurriedly adjusting the positioning of the coating head so the flow spans the film base correctly. Then you let it run until the whole loop is coated and stop the pump and pull back the head before it tries to lay more emulsion down on what's already been coated. Whew!
Long story short, we were able to do this, and hung the film to dry. It's usually dry in a couple hours and can be slitted and perforated. Oh, did I mention that Mark managed to cadge a small research-level perforator that was being disposed of? Well, yeah, not something that just anyone can get their hands on. We didn't get to that part while I was there, but next time I'm over I'll ask for a demonstration of that.
Anyhow, thought you guys might find it interesting. Below I've included a few snapshots from the week:
Precipitation of the silver into the salted gelatin:
The acetate film base, obtained from Ilford, for testing:
Mounting the film base on the coating machine and splicing it:
Mark, with the coated film base after the fun:
