I've been having a back and forth experimentation discussion here on Flickr about why bands sometimes appear on my 4x5 sheets when I develop it at home. You can see it in the previous shot I posted.

As I wrote in my discussion of the popular 'taco method' of developing large format sheets in a tank, I followed the suggestion of using hair bands to keep the sheets in their taco shape.

Using straight elastics is right out since the elastics are too tight to the sheet and don't allow chemicals between them and the sheet. I tried elastics once and they definitely show up.

Anti-Halation Layer

Or they don't allow the sheet's antihalation layer to be rinsed off. One of those two.

The antihalation layer (AH layer) in some films traps light that passes through the emulsion and prevents it from being reflected back into the emulsion again. That layer should be washed out in either the presoak step or the end rinsing / washing of the film after developing and fixing. You can usually see the AH chemicals being washed out when you dump the presoak. On Kodak films it is blue liquid looking like antifreeze (I wouldn't drink either).

Shifting of bands during development

As I note in the discussion, it doesn't appear in some sheets and appears in some others. If it is random, as I suggest, perhaps it is due to the bands being shifted during the development in some sheets and not in others? Since the sheets more or less jumble around inside the tank during agitation, then it may account for why it appears in some and not in others.

Or the type of hair bands?

Or a combination of that and that I'm using the wrong type of hair band. The fabric of the hair band should allow enough chemicals and wash to get through to the AH backing. But perhaps other types of hair bands will allow more 'breathing'?

More experimentation to come.