I’ve also noticed that 35mm and 120 differ in the amounts of photo flo they each need.
A good test is to take a dummy strip of film, even just a section of film 8” long or so and pour some distilled water into a container. Add one drop of photo flo or whatever surfactant you’re using. Dip the strip in, pull it out and hold the base side up vertically to light and see if the water is running off in streams, leaving droplets on the film. If so, add another drop and repeat. You want to do this until you find the minimum amount of drops that when held to light show an even sheet of water flowing off the base side of the film.
I did this test and for me it’s 5 drops to 500ml of distilled water for 120, and 20 drops for 35mm. Also I’ve found a 120 film like delta 3200 requires more surfactant to create the sheeting action.
My water is very hard and I struggled for years to get perfect negatives. After the wash I fill the tank with Distilled water and agitate 20 times, let the tank sit one minute then dump. Repeat this one more time then dump. Then I move on to my photo flo. I then hang 120 (what I mostly shoot) at a 45 degree-ish angle. 35mm I hold up at an angle for 30 seconds or so then hang vertically.
Bottom line is no surfactant (distilled water only final rinse) puts you at risk for differential drying marks. It’s when the emulsion is stressed during the drying process which creates extra density. This is due to droplets or runs of water remaining on the film after the areas around it have dried. Thus the need for a surfactant to help “sheet” the water off the film evenly.
Too much photo flo can leave milky appearing marks which can be removed with a weak stop bath then re wash.
Hope this helps.
A good test is to take a dummy strip of film, even just a section of film 8” long or so and pour some distilled water into a container. Add one drop of photo flo or whatever surfactant you’re using. Dip the strip in, pull it out and hold the base side up vertically to light and see if the water is running off in streams, leaving droplets on the film. If so, add another drop and repeat. You want to do this until you find the minimum amount of drops that when held to light show an even sheet of water flowing off the base side of the film.
I did this test and for me it’s 5 drops to 500ml of distilled water for 120, and 20 drops for 35mm. Also I’ve found a 120 film like delta 3200 requires more surfactant to create the sheeting action.
My water is very hard and I struggled for years to get perfect negatives. After the wash I fill the tank with Distilled water and agitate 20 times, let the tank sit one minute then dump. Repeat this one more time then dump. Then I move on to my photo flo. I then hang 120 (what I mostly shoot) at a 45 degree-ish angle. 35mm I hold up at an angle for 30 seconds or so then hang vertically.
Bottom line is no surfactant (distilled water only final rinse) puts you at risk for differential drying marks. It’s when the emulsion is stressed during the drying process which creates extra density. This is due to droplets or runs of water remaining on the film after the areas around it have dried. Thus the need for a surfactant to help “sheet” the water off the film evenly.
Too much photo flo can leave milky appearing marks which can be removed with a weak stop bath then re wash.
Hope this helps.