Originally posted by Steve Beswick I think you are over selling this a bit. The Wikipedia page you should be linking to is for celluloid, not guncotton.
Celluloid - Wikipedia
Yes, celluloid film is far more flammable than acetate film, but that doesn’t mean run in fear from it. The big concern with celluloid film is in prints of movies, specifically playing them, not a strip of still image negatives. A few negatives in an envelope are not going to spontaneously combust.
I realize that your intent was to promote safety, but by overstating the hazards of celluloid film you are spreading FUD, this time at the risk of old family negatives being disposed of in waves. This is the internet after all, and the internet loves to get excited about random things.
Now as far as the folded negative is concerned, I agree that speaking with a professional is a very good idea, and that cutting is a very bad idea. Old negatives, even acetate ones, can be very brittle. Therefore the water bath sounds like a good idea, but I’m hardly an expert on that one. I would definitely caution that warm water should mean not much warmer than around 80 degrees Fahrenheit. Much over 80 degrees even modern emulsions start getting very soft.
I disagree with your assesment of my post and your strange assertion that I am somehow spreading FUD.
The page I linked is correct (yours is not as relevant or informative!) and from the UK Health and Safety executive and while it may be seen to be applicable to large collections the principles outlined are sound.
The issue here is twofold the film type/base itself and dealing with the fold.
First the film, we really do not know if it is cellulose nitrate or safety film cellulose triacetate a plastic base. The former was used at least in professional film until around the early 1950's.
The HSE document linked to was not to cause FUD but to help the OP identify the film. Rather this than be complacent IMHO!
The only film that I have seen that I am sure of being cellulose nitrate has been old X -Ray film; brown and blistered surface. Which was carefully copied and the old film discarded.
It does not seem unreasonable to me to understand what you need to do or be aware of if the film is identified as cellulose nitrate.
There is no suggestion in either my post or the link that one should panic. Rather there is a very reasonable suggestion that if the film has viewable images to contact a conservator/film archive for advice on preservation.
I would also caution about the use at this time of any water bath (at any temperature) until you know what you are dealing with; it is quite disconcerting to see the image slide of the substrate unless you have an alternative substrate to slide it onto
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Of course non of this matters if the image is of no real value sentimental, historical or otherwise to the OP