Diagnosing light edges on images (dark edges on negatives)

Since I’ve started developing my own film, I’m pleased to say I have yet to ruin any of the dozens of rolls of film I’ve processed at home — every single roll has resulted in usable negatives, with seemingly proper density. However, something has been dogging me, and I only recently discovered that it was my own fault: Images with light edges (on the positives), dark edges (on the negatives).

At first, given the way that these edges presented themselves, I immediately assumed that there were light leaks, probably from the camera backs, or perhaps the dark slide slot in the case of my Hasselblad. Here are a few examples of what I was seeing:

Particularly visible example of this issue, but seemingly on the right edge only (or at least is only noticeable there). Copyright © 2019 Wesley King
Lightness on both edges. Copyright © 2019 Wesley King
Both edges, but mostly on the left. Copyright © 2019 Wesley King

Some random observations (and you can see why and how I was a bit confused):

  • I initially concluded there was a light leak, but after replacing the light seals on my Yashica Mat-124G where I’d noticed the problem appeared to be most pronounced, I didn’t actually see any difference.
  • Some rolls presented the problem; others didn’t. That made me think there was a problem with specific cameras, although I couldn’t quite find the common thread at first.
  • It seemed that the problem was only on one edge in the case of some of my Hasselblad shots, leading me to think of the dark slide light seal.
  • Sometimes I didn’t notice the issue at all, sometimes it was pronounced, leading me to think it was the shooting conditions (e.g., bright light vs. subdued light).

Alas, I was seduced into the entirely wrong path. What key piece of evidence was I failing to connect? What critical item was I missing? There is just one, and it was critically important:

  • The film rebate — the very edges of the film strip with the brand and exposure number markings — would be dark as well (on the negatives) if there was a light leak. They were not dark; only the image area was, so this couldn’t possibly be a light leak, and I was essentially chasing my tail.

While I’d Googled this problem before inconclusively, I decided to dig a little deeper, and finally unearthed the nature of the problem: This is not a light leak issue, this is an uneven development issue.

What was actually happening

So, how on earth was I getting uneven development of my film, edge-to-edge? Well, since starting to develop film at home, I’ve been using the popular Paterson tank, agitating the film with the “swizzle stick” (technically what Paterson calls an agitation rod) rather than full tank inversions. I had three reasons:

  • I was wary of over-agitating and over-processing and causing overly dense negatives; the swizzle stick seemed a way to avoid that because it’s considerably more gentle (depending on how you do it, I suppose).
  • I wanted better control and consistency, and the swizzle stick seemed to provide that vs. the more violent motion of inversions.
  • I always have trouble getting the plastic lid on and off the tank, and of course, while developing, the clock is literally ticking.

The problem is, I was being too gentle — at least part of the time. If you think about the film, the design of the reel itself, and how it sits in the tank, and then apply a little logic, it seems obvious (in retrospect) that the gentle twists of the swizzle stick will introduce a stronger chemical refresh at the top and bottom of the reel, where it’s open to the chemistry in the top and bottom margins of the tank, and where the movement of the liquid is freer, and more turbulent. At the center of the film, there’s simply not as much movement and not as much refresh, since the spiral has a relatively small gap between each successive layer of film, and nothing is forcing fluid through from the top or bottom.

The end result? The edges of the film were being developed more strongly than the center, resulting in uneven development, with edges darker on the negatives, and lighter on the corresponding scans (or prints if you’re into that). The fact that it was more pronounced on certain rolls than others suggests differences in film, processing time, or most likely, variations in my own technique and action — all of which could serve to amplify or minimize the issue.

Then what?

The real solution to this problem could have been more aggressive use of the swizzle stick, or perhaps tilting the tank a bit while using it to distribute that turbulence better. Some people swear by using the stick, and perhaps there are techniques (whether what I just suggested or something else) that ensure better distribution than I achieved.

But for me, just switching to tank inversions was the right answer. This seems to be the stuff of religion among film geeks, and I’m not going to wade into that debate; at the end of the day, the technique that works for you is the right technique. But it’s clear that for me, I’m not getting the optimal result from swizzle stick agitation, so I decided to switch to inversions.

Tank inversions clearly force liquid in and out of the spiral through the top and bottom, ensuring that the entire surface of the film has a more robust exchange of fluid, and that developer is thoroughly redistributed as the chemical expends some of its potency while the film develops. The risk, of course, is that this robustness exposes the film to too much developer action, risking the negatives becoming too dense. But most of the materials I’ve read online suggest that use of the swizzle stick vs. gentle inversions (i.e., not inverting like the tank is a cocktail shaker) shouldn’t require different development times. But like anything with film developing, variations in technique will produce different results, and some experimentation may be required.

Once I’d made the decision to change my approach, the next step was to go back to the specific films where the problem was most obvious. Based on what I’ve read, this issue can affect certain film stocks more than others (although I can’t quite envision why or how), so it made sense to target the ones where I’ve seen it most: Bergger Pancro 400, and the various Fomapan options. The problem is that not every roll of these films exhibited the issue, so clearly it’s far less about the film, and far more about me, and the technique I used during development. But since Fomapan is inexpensive, has a shorter development time than Bergger Pancro, and I have an enormous stock of Fomapan 400, I decided to test first with that. And just to reduce the variables, I put it in the same camera where the problem was worst, my Yashica Mat-124G (even knowing that wouldn’t truly matter, but trying to be scientific here).

After switching to four gentle tank inversions each minute during processing, instead of four back-and-forth twists of the swizzle stick, not at all surprisingly, I got perfect results with even density edge-to-edge, no dark edges (negatives / light edges (positives), and the beautiful image quality I’ve come to expect from Fomapan. My negatives appeared slightly more dense, perhaps, but still within a range I’d consider normal:

Two of the images look a bit dark, but they represent the actual shots. No dark edges!

Here are a couple of representative scans. No light edges on either one — or indeed, anywhere else on the roll.

“Out of View” Copyright © 2019 Wesley King.
“Denver” Copyright © 2019 Wesley King.

Basically, problem solved.

Unrelated to this problem, but I’ll bring it up in the same breath just the same: I’ve stopped squeegeeing my negatives. Like agitation during development, the use of a squeegee is subject to strong feelings and political-grade debate. As with agitation techniques, whatever works for you is the right answer, but I’ve experienced far too much scratching from using one, no matter how well-prepared and careful I was in using it. My new technique is to remove the reel from the center carrier, then (very!) vigorously shake it numerous times after the surfactant step (i.e., Photo-Flo), flip it around, and shake the heck out of it again. Then, remove the film and hang. So far, I’m very pleased with the outcome. No scratching, evidence of rubbing, and far fewer emulsion anomalies (little dots in the scans).

The moral of the story

I suppose that if there’s any moral to this story, it’s one I’ve already learned with the (real) light leaks in my Yashica A: Things are not always as they might appear.

I don’t regret replacing the seals on my Mat-124G; they were completely shot, a sticky mess of deteriorated foam goo. But they had precisely nothing to do with the problem. With film, there are so many variables, and I completely fell into the trap of what seemed so obvious (light leak) without considering how an actual light leak would present itself (it would be on the film rebates too).

Alas, film photography is full of learning opportunities, and it’s part of what makes the hobby so enjoyable.

Happy shooting, and whether you prefer to swizzle or invert, happy developing.