scrapparts said:
Thanks for all the added info.
One more question though. How can you tell the new types of film vs the older types?
scrapparts
Hold a cigarette lighter flame briefly under a clear area of the developed film. The "wet" film will be unaffected and, with the "dry" film, a black spot will appear. Don't hold the flame close enough or long enough to burn the film - this takes a little experience. It only takes about one second or so, with the tip of the flame about 1/2", or so, away from the film.
Another testing method is to put a small piece of the black area into a small amount of liquid laundry bleach (or 10% v/v HCl). The "wet" type will strip, but the "dry" type will be unaffected (will remain black). This method was given by our old forum friend, Juan Manuel Acros Frank. I haven't tried it as a test method but, from my experience with bleach on "wet" film, I'm sure it works.
Modern catscans are usually the "dry" type but regular x-rays can also be "dry."
To the eye, developed "wet" and "dry" film look identical. Whereas "wet" film is easy to process, "dry" film is almost impossible. The silver behenate compound on the "dry" film is unaffected by just about any practical chemical I know of. I have been able to put the silver into solution with boiling 25% nitric acid, but that is not practical at all. Unfortunately, when you get a batch of developed medical x-ray film, you will find a mixture of "wet" and "dry" film that you cannot readily sort and separate. This has made the processing of medical x-ray film a difficult thing to do.
It is interesting to note that UNdeveloped "dry" film is almost fully transparent. It appears as a clear blue (usually) plastic with a very slight haze to it - you can definitely see through it. It looks like "wet" film that has been totally stripped. It doesn't turn black and opaque until heat is applied to it.