What To Do?
If you hadn't noticed, I've written a quick and dirty guide to developing your own black and white film at home. If you haven't checked it out, go do so now. The last part of the development process is rinsing the film to remove the remaining chemicals and then a final wash in a rinse aid, like Photo-Flo.
A conversation I was having with someone on Facebook led to the question, "What can I do if I have washed my negatives and they have drying marks on them?". I thought about this - and I've experienced it before myself. It's a really frustrating thing, and there isn't a single standout course of action.
Why does residue form on home-developed film?
Residue forms on the film due to mineral deposits in the wash water that are left on the film when the water dries.
Rinse aid (essentially a surfactant like dish-soap) reduces the surface tension of the water to allow the water to move freely off the film before it dries and deposits the minerals.
When too much rinse aid is used, bubbles can form that - rather counter-intuitively - trap the residue.
When too little rinse aid is used, the water cannot slough off the film quickly enough before it dries and deposits the mineral scum.
Should you re-wash your film or not?
The first thing is - if you haven't cut the roll into strips and it is still hanging, it's quite easy to fill a tank or basin with distilled water and add Photo-Flo again, and then run the roll through the rinse solution again.
Hold the film at both ends preferably with the film clips still attached, with the shiny (non-emulsion) side facing the bottom/sides of the tank. Using a rocking motion, dip the film into the rinse solution, and then move your left hand up and right hand down, then left hand down, right hand up, repeating a few times. Remove, shake the excess off and hang. Always squeegee - only with gloved hands (marigolds work well for this) - to ensure there is minimal residue likely to gather.
An alternative solution to cleaning drying marks on your film
If you have - then it's still possible to re-wash, however it's quite annoying. In those instances, I might recommend a solution called "PEC-12" (photo-emulsion cleaner). Along with the fluid, the company sells a pack of lint-free pads.
Squeeze a couple of drops (no more) onto one of the pads, fold it in half, then, holding one end of the strip with a pair of tweezers, run the strip through the pad. The pad folded over should cover the whole of the emulsion and backing sides of the strip allowing you to clean in one motion from end to end.
Bear in mind that if you use too much PEC-12 fluid, it will leave its own residue on the film, so be more sparing than liberal.
Conclusion
At the end of the day, when developing your film yourself at home, you should aim to use distilled water for the final rinse only (where you add the Photo-Flo). You do not need to use distilled water for any other solution.
This would minimise the likelihood of mineral deposits being left on the film as the water dries, should you use too much or too little Photo-Flo.
If you do manage to find drying marks on the film after it's dried, if you haven't cut the film into strips, simply re-wash in a new batch of Photo-Flo solution.
If you have cut into strips, you can use a solution called PEC-12 and some PEC pads to gently wipe the marks away.
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