ibcrewin
Ah looky looky
Just last weekend, I put 4 rolls in a tank and one roll came out completely blank. Totally developed an unexposed roll 
Pirate
Guitar playing Fotografer
I've got a roll of Efke 25 I'm not sure is exposed or not. I don't want to run into the same thing! I have a bad habit of leaving the leader out when I'm done shooting a roll so I can cut it and clip the corners before I develop it, but when I'm juggling things around and lose track of a roll before I've clipped it..... bad things can happen. Ugh.
ibcrewin
Ah looky looky
That's EXACTLY what happen to me. Do a little clip test.
Tim Gray
Well-known
Buy a film leader retriever. Then you can rewind the leader in the canister when you finish a roll. When it comes time to develop, pick the leader out with the retriever, trim, and go about your business. Spend the dough and get a plastic one; the cheap metal ones aren't so hot in my opinion.
At the very least, fold over the leader and crease it when you finish a roll so you know it's been used.
gliderbee
Well-known
I always keep the leader out for the same reason, BUT I fold it a few times before putting it in the cannister, so it's always recognizable as a exposed film.
Stefan.
Pirate
Guitar playing Fotografer
I never thought to fold the leader or crease it. That's so simple! Ok, I'll do that, and hopefully won't have this problem again!! Thanks!
Ezzie
E. D. Russell Roberts
I know what it feels like. I've just wasted three rolls of 120 Acros100. They were for the most part completely opaque. Strange thing was that one or two frames on each turned out OK. Where to begin? Overdeveloped theory: New film not yet tested in Caffenol? Overexposed theory: Unfamiliar using new light meter in bright light conditions? It took me three films to find the culprit. The shutter sticks! And now I know what grossly overexposed negs look like. In my case, with the camera in question, for one thing you can see evidence of light beginning to stray outside the confines of frame.