Bits & Pieces

 Site Index 


Emulsion Geek #1: Repellency Spots, aka 'Comets'

March 18, 2011

Repellency spots are about the only real bugaboo with coating film. From reading various sources, I think it is one of those issues in emulsion making that is more trial and error and case-specific than seems called for, but it is what it is. I'm closing in on satisfaction with the one emulsion I've worked with on film so far. When I try a new emulsion, the comet solution might be different. Time will tell.

Although they can show up anywhere, comets tend to congregate at the edges of the coating path. This is one of the reasons to be open to cutting a narrower format if need be. One could also just make a policy of coating extra wide, but that's a little too wasteful of emulsion for my sensibilities. If I didn't have a couple of different format cameras to play with, I might feel differently.

I've always bracketed exposures. Seemed like cheap insurance. But bracketing has even more utility with handmade film. If one exposure has flaws, the other is likely OK. In this case, I'd have preferred to print with the exposure that ended up with the comets, but the denser one worked out. Of course, you could always bracket with identical exposures.

A side note: the film strip was a little off-center in the camera. That's why the bottom doesn't have an unexposed edge. (Fuji 690III 90mm, 1 sec @ f/8 and f/5.6)

Making and Coating Photographic Emulsions, by V.L. Zelikman and S.M. Levi, 1964 English Edition Focal Press Limited, pp 261-262.

Copyright © The Light Farm