C-41: Emulsion flaking problem
I've been doing C-41 processing for about a year (a few dozen rolls total) and have recently run into a problem: On three of my last four rolls (all 35mm), there are small flaws in the emulsion. Here's a sample scan from an affected negative, as scanned at 2700 dpi (219x192 crop; it's not huge) with a Minolta DiMAGE Scan Elite 5400:
This scan's colors have been reversed, so the flaw shows up as a black spot. Looked at under a loupe, it looks as if the emulsion has flaked away. I've never encountered this problem before. The films are all different types (Kodak BW400CN, Agfa Vista 200, and Kodak Portra 400VC). They were processed in two batches (the BW400CN in the first, the Agfa and Portra together in another batch), with one intervening roll that didn't exhibit the problem (another Agfa Vista 200). All were processed in Paterson Photocolor II developer with Kodak bleach and fixer. I've been replenishing the bleach but the developer was fresh for the bad rolls (that is, freshly mixed from the same original bottle). I use a manual stainless steel tank (no machine processing) and a water bath to control temperature of the chemicals. For washes between steps, I use flowing tap water at hand-judged temperature.
So, any ideas what might be causing this problem? I've got several, such as bad bleach and temperature-control problems during washes, but I thought I'd ask for advice here before experimenting on my next few rolls. Thanks.
Do you use (cheap) glass bottles to store the C41 developer? I once had a similiar problem, and it turned out that the developer (highly alkaline, I guess) "corroded" the glass, which resulted in a lot of glass flakes in the bottle.
I never had this problem again, after puring the developer through a paper (coffee) filter immediazey before use.
Thanks for the suggestion; I hadn't considered this possibility. I am using glass bottles, and if the developer might cause a few glass chips to break loose, they could conceivably be wreaking havoc. My stock solutions are currently in Boston rounds, but I mix my working solution into a larger Snapple bottle (long since devoid of actual Snapple, of course).
The pH of C41 developer is ~10.5. This is not high enough to affect the bottles unless the glass is extremely poor quality. Normal glass is not etched until you get to the pH 12 - 14 range.
Etching could take place with very long storage times, but considering the lifetime of a color developer, this does not usually happen. It would probably take a year.
I would think that other solid contaminants would be likely, but they would normally not rupture an emulsion the way this spot appears to look. It looks like something pushed up from inside the emulsion.