I would appreciate some help with a problem I have when using plastic spirals. On a roll of ten 6x7 film I have a dark band on the eighth negative, always within a little in the same place. I have considered all sorts of possibilities, and have come to the conclusion that the end of the film is curling in and touching another part of the film (ie where the 8th negative appears). None of my personal contacts have encountered this, and I've so far been unable to find anything on the internet. Does anyone have experience of how to overcome this? I am unable to post a scan.