Quote Originally Posted by yanboechat View Post
When I developed FP4+ I put 2 rolls in the same tank. One came with the marks, and the other not. Both rolls got the same soup, same water, same final rinse.
Did the two FP4 rolls come from the same bulk roll, or were they bought at the same time from the same place? If the former, they're definitely from the same batch and if the latter then it's highly likely. Either way points to a processing issue rather than material. I don't know how the batch number is displayed on the film (probably bar codes these days) but if you could find something that looks like a batch identifier and they are both the same, perhaps you could go some way to ruling out the material.