How to determine the service life of photographic film?

The base of photosensitive film is mainly acetate, and the gel emulsion containing surface silver (a photosensitive chemical) and coupler is coated on it layer by layer. What is the reason for the aging of photographic film, that is, what determines the service life of photographic film? On this issue, we consulted the after-sales service center of Kodak Co., Ltd. in Japan. "The service life of photographic film is generally 1~2 years from the date of production. The direct cause of film aging is that silver halide will change chemically even if it is not sensitive to light. Color film is more prone to chemical changes than black-and-white film, and high-sensitivity film is more prone to chemical changes than low-sensitivity rubber film, so its service life is shorter. In fact, even in the service life, the film has undergone a little chemical change, but its influence is invisible to the naked eye. With the gradual progress of chemical changes, the film sensitivity will decrease in turn, the concentration (minimum concentration) of unexposed parts will increase, and the color balance will change, thus affecting the quality of the film. " Then, what about the film that has been exposed but not developed? Generally, after a photo is taken, the film will be left for several months before being developed. Even if it is still in use, the effect of the photo will become worse. "This is because the latent image (invisible image) formed by silver halide particles on the film will gradually weaken and the sensitivity will decrease. If it is left for a long time, the color balance will also change. So develop the film as soon as possible after taking photos. If it can't be developed in time for some reason, or if you buy too many films to use at one time, you can temporarily store them in the refrigerator. Remember never to put it in the refrigerator, because the hot air or moisture in the refrigerator will promote chemical changes, so it should be kept in the freezer. But storing in the refrigerator can only slightly extend the service life, not for a long time. "