Making Roll Film
March 17, 2011
Allowing for some minor differences, Melinex 535 film coats just like paper. On the plus side for film, although paper buckles when it gets wet, film stays flat. On the negative side, repellency spots (aka 'comets') are very easy to control on paper, but a bit more of a problem on film. I've made four batches of ten rolls, and with each subsequent batch I've come closer to comet-free coatings. This last batch had six comets on ten rolls. I bracketed each shot and had no problems getting a good exposure for any given image, but it's always fun to strive for better. I'll post my exact surfactant protocol as soon as I'm satisfied it's the best I can make it.
The mechanics of coating are pretty straighforward. Before starting the last step of emulsion-making, I stack ten sheets of 9"x 36"x 1/4" glass, each with a 7"x 35"strip of 535 and a clamped-on square wood dowel to serve as a coating well guide bar. I have a second area that's dead level for stacking the glass after I coat each strip.
All of the work can be done by the bright light of red LED's (I use a string of red Christmas lights.) There's no stumbling around in the dark.
After the coated strips have dried, they get cut up into appropriately-sized strips. I have the same general philosophy as Kodak did back in the day.
"...Eastman still concerned himself with cost-cutting innovations in the production area. For example, different lengths of film were placed on the market, including rolls of film with only six, eight, or twelve exposures, so that there would be less scrap on the ends of two-hundred-foot sheets of celluloid."(Images and Enterprise - Technology and the American Photographic Industry 1839 to 1925, by Reese V. Jenkins, The John Hopkins University Press, 1975, p 149.)
I have a couple of 127 and 828 film cameras. 127 film is only 24 inches long, rather than 120 film's 32 inches. 828 is even shorter. If a particular strip of film didn't coat well for a full 32 inches, it can be cut for a smaller format.
("Making Roll Film"to be continued.)
