4x5 sheet film developing problem.

I wish I had a scanner so I could show this better, but I'll do my best to explain. Here's the scenario. I just developed 6 sheets, 3 turned out "perfect" (well...at least they didn't turn almost completely black) where the other 3 turned out almost black. I'm usually pretty good at trouble shooting, but I can't find answers for this because it's all of the same subject with the same filter, the same film, the same time of the day.
The negatives that are black look like I developed them for WAY too long (but my times are right, the dilution is right because the other film turned out good). there are the usual clear borders around the edges, so it can't really be a loading problem. My exposures were all the same, so I couldn't have exposed them (unless I shot 3 fully opened after focusing, which I doubt I did 3 times in a row). The thing is that I shot with different lenses as I just got a whole new system and all the pictures that were black were with my own homemade lensboards that I made out of matting (white) and I did a half-assed job with a sharpie to make one side (the inside) black. Is it possible that this could be the cause? Any other suggestions?

Light leak and fogging seem a probable cause with your lens boards, and one you should investigate first I think.

Shoot and develop 2 more sheets, one with each board to be sure but it sure sounds like the home made lens board and the sharpie will turn out to be the culprit.

is it possible that your film was corrupted pre-exposure? that is an odd problem.

I make temporary lensboards using solid matte black art cardstock. Here's why:

Put your white foamcore lens board back on the camera. Aim at a bright light. Remove rear standard from camera. Drape dark cloth and stick your head in the back of the opening. What do you see? (wait a minute for your eyes to adjust). Yep - even with the sharpie foamcore is translucent. Matte Black paint will help, but next time use matte black art board.

My mistake too, at one time.

NWG

could it be that you forgot to close your lens down?

Tommy5c: This isn't possible, because the other film I used of the exact batch at the same time is perfect.

nawaqi: That's the most likely answer. I just tried your experiment and you're dead on. Light does bleed through, although it's very faint. I've loaded film in my bathroom when my girlfriend turned on the lights outside the room, allowing light to come through the cracks and the film turned out fine. Would this little amount really cause that kind of problem? However I also realized that when I took the picture the lens was pointed down and the board is somewhat flimsy, so it's very possible that light can get in that way as well. The sun was also at an 85 degree angle directly infront of me so that would make it a lot more light than just a lightbulb.

Eric: I was thinking I didn't close my lens down, but what I can see from the photo is still in focus. It's hard to describe my setup, but I was up against a fense, shooting through the links and only using two of the tripod legs. The camera was constantly shaking until I held it firm during shutter release, so I doubt that would be it, but it was a very possible explanation.

I ordered a couple more metal lensboards and should have them in next week to hopefully stop this. If not, it's back to the drawing board.

Thanks guys for your help. You've saved me a lot of time, agony and money. I'm so thankful this forum exists.

I think it has to be the lensboards. Another thing I can think of is that you pulled out the darkslide facing the ground glass, but I think you would have noticed that, especially if you did it three times. Hey test your lenses too, make sure they're all stopping down properly and that the shutters are calibrated.