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I realize the only way to get a definite answer to this question is to develop and find out, however I am inquiring more along the lines of the light-proofness of film holding bags.

I was loading sheets of HP5+ into 4x5 holders and upon loading and locking the holders I turned on the light in the space I was in. I noticed that I had left the film inside of the bag with it folded and resting on the table outside of the two-part box. Are these bags generally light-tight when folded over?

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    What happens if you shine a torch through from the inside of the bag to the outside when you're in the dark room? Can you see any light from the torch through the bag? – laurencemadill Jan 29 '16 at 9:44
  • I did find a pinhole-sized spot along the seam. I suppose I'll just get a replacement box and save this one for some less important work. – user1560249 Jan 29 '16 at 14:50
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    That's going to be your safest option if it's important work...but depending on folds in the bag etc you might be ok. – laurencemadill Jan 29 '16 at 14:52
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    i think it will probably be ok. – Alex Feb 19 '16 at 8:50
  • Go to Shippers Supply and get an Artline 400 black paint pen. Using a strong light, search for pin hole light leaks, and as you find them, daub them with the paint pen. – Sherwood Botsford Mar 9 '16 at 16:21
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Process a sheet from the top (check the notches). Look for a light strike. If you don't see any, then you're probably good to go. The back has a light absorbing/anti-reflection coating and is less likely to have a problem than the top sheet. Either way, remember that the light strike is not image-forming and cannot compromise your image unless quite fogged in a shadow area of the shot.

To hyper-sensitize film, I used to fog it in a controlled way so that any extra exposure in the camera was enough to pull stuff out of the shadows. Film is great stuff.

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It can depend on how the light-tight bag is made. Black and lined and a double zip is usually light proof. If the film was outside the double dark slide and you were hoping to use it in a critical shoot, I would discard it and accept the cost of the error rather than use it and risk ruining the image. It won't be an error that you will make again. As a precaution, you should load an exposed piece of 4x5 inch film into a double dark slide in the light.

Do it until you are certain how to do it without error and then do the same with your eyes closed. You should do this enough times until you are faultlessly loading the film. Still using the exposed film, you should do it in the light-proof bag until you are faultless and then finally turn off the lights and do it until faultless. This practice may seem tedious to you but if you are using a client's film and they only provide one piece for the shot, you cannot afford to make this mistake.

Hope this helps

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