There are many ways to approach this problem. So, I offered a helpful hand from my bag of tricks, and now, above, I offer further information to you to explain in more detail. In high humidity, if the silver is toned or otherwise made archival, the gelatin is the thing that is attacked, and if you lose the gelatin, having a perfectly toned archival image is useless when you see the ugly traces of mold or fungus in the gelatin. One thing to consider is that handeling negatives introduces these biological contaminants and the paper sleeves that we often use also introduce them, so the formalin also 'protects' against this sort of contamination. The benzoic acid is relatively stable, but nothing lasts forever. The false sense of security is that this will protect you forever. The film is essentially sterilized by this treatment as you remove any spores and prevent any activity for some time to come. Therefore there are few sites left for formalin to react with. If the film were unhardened, then the gelatin would, as Ryuji says, suck it up rapidly, but this is not the case we deal with regularly. Packed in sleeves this can be quite long. The half-life of formalin in a B&W coating which has been optimally hardened already is as long as it takes for the formalin to evaporate. The optimum range for benzoic acid is pH 3.5 - 4.5, but it will protect even on the alkaline side (ever see "sodium benzoate added as a preservative" on food labels? Yes, it even works as the sodium salt on the alkaline side, it just takes a bit more.)īoth benzoic acid and formalin have the capacity to kill any spores present in the film or in the final rinse itself. This was a well known secondary purpose for formalin in stabilzers.īenzoic acid supplies just a trace of acidity at that level and as it dries down in the coating the pH becomes slightly more acidic, but it has no buffer capacity to speak of and so will not harm the film or paper support. You can always rewash the film to remove the benzoic acid.īoth benzoic acid and formalin were used for years in Eastman Kodak stabilzers for their activity against fungi, mold and bacteria. If you prefer, don't use the benzoic acid, just use the formalin. If there is excessive tackiness, lower the level of benzoic acid in the final rinse until the tackiness is acceptable or vanishes. The benzoic acid does sometimes increase tackiness depending on water supply and film characteristics. If it is too tacky to suit you, just rinse and then restabilize as noted below. Please test the final dry film for tackiness before storing if you used benzoic acid. I only suggest the above if you live in the tropics or in areas of high heat and / or humidity. I know, formalin is a no-no, and I recognize that, but it is no higher in concentration above than it was in C41 or E6 stabilzers and if you accepted that, I would be remiss in not mentioning it here. These are very good 'bug' killers that help protect films from mold, mildew, fungus and bacterial growths in damp or humid environments that can lead to film deterioration. (you can go lower - see below)Īdd 3 ml / liter of 37% formalin to the final rinse. Here are things you can do to improve film quality if you worry about fungus and mold.Īdd between 0.5 g/l and 1.0 g/l benzoic acid to the final rinse. I wish to add a little note off the previous post. This is probably the most useful invention I made in 2005 that people around me appreciated the most.) I use Triton X-100 or PhotoFlo to wet mops to wipe my darkroom floor, or mix windshield washer fluid! (Surprisingly, I could formulate a windshield washer fluid that does not freeze even in this f*cking cold Boston winter. I have a custom blended surfactant that doesn't bubble like PhotoFlo and lets the water go down the film surface very quickly without leaving bubble mark. It's an ok wetting agent but there are better ones that have less biological toxicity. I personally don't use Triton X-100 or similar surfactant. (Propylene glycol is not as hygroscopic as di- or triethylene glycol, which is less hygroscopyc than glycerol.)Īs far as I know, PF6 don't contain propylene glycol. A surfactant like this doesn't mix with water at an arbitrary ratio, so for PhotoFlo 200, there is a need for an organic solvent together with water. They are based on Triton X-100 (aka octylphenol ethoxylate, yet another name of the same compound you mentioned) but they differ in concentration.
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