Expiration date on film

ksklo

Well-Known Member
I have always been curious about how much attention we should pay to the expiration date st&ed on the film packing. Does it matter if film is kept in the freezer or not? And would it be able to maintain its expected image quality if it was used not too long after its expiration date, say a few months? Finally is there any difference on the results with regards to negative vs. slides?
 

daleh

Well-Known Member
> If film is kept in a freezer, it will be "fresh" indefinintely when thawed out. Film refrigerated at 40 degrees will remain "fresh" for years. The expiration date is conservative for most films and takes into account that most will store film in varying conditions. It is actually far more significant as a reminder to retailers to rotate stock on a regular basis. Anytime you can buy either frozen or refrigerated outdated film, it will be a bargain. Caution however, come "professional" films are more sensitive than others and may pick up some base fog or gain some speed shortly after expiration if stored in ambient conditions. These usually have some kind of notation on the package. Also, beware of latent image fade. If exposed pro grade film cannot be immediately processed, it should at least be refrigerated to retard latent image fade.
 

pecker

Member
> According to many pros the dyes used in color film, both negative and positive, mature over time and reach their peak at the time of their expiration date (very subjective, of course). This process of maturation can be significantly retarded by refrigeration and virtually halted by freezing. A chemical engineer and executive for Eastman Kodak told me years ago that off-the-shelf consumer grade film can be optimized by using it closer to the expiration date and that professional grade film has been optimized for immediate use, which is why most is sold refrigerated. I have not read or heard anything lately on this subject, but this is how it was explained to me twenty or so years ago.

Doug
 

daleh

Well-Known Member
>The primary damage that is done to any film sitting, either exposed or unexposed, is what is called "dark reaction." Dark reaction is the same thing that happens when you expose film to light, only much, much slower. It results in base fog and apparent increase in speed. Base fog diminishes the contrast range of the film. Since color film has at least three different light sensitive emulsions and dark reaction does not proceed at precisely the same speed on each, outdated color film will also experience a color shift as it ages. With color negative film, unless this is far advanced, it can be corrected in printing. Slides, of course will look off color but can also be printed and color adusted either with Photoshop or automated printing analyzers. The effects that the Kodak person were correct but his explanation was technically faulty. The problem is not the dyes but the dark reaction affecting the silver emulsions which only during processing are converted to dye. This is true of negative and transparency films. He is correct that the production and dating on consumer films presumes some color shift before the film is actually exposed and processed. Same for his explanation for pro films.
 

jim0266

Well-Known Member
From

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Refrigerating camera films reduces the photographic effects of storage, but refrigeration cannot reduce the effects of ambient gamma radiation. Gamma radiation (high energy from cosmic radiation and low energy from radio-nucleotide decay) increases the D-min densities and toe densities and also increases grain. Higher speed films are more affected by gamma radiation than lower speed films. A camera film with an EI (Exposure Index) of 800 has a three times greater change than an EI 200 film. Exposed and unprocessed film that has been properly refrigerated retains the speed and contrast of the exposure conditions, but the overall D-min, toe and grain will continue to increase.
 

daleh

Well-Known Member
> How significant is ambient gamma radiation. Since films many years out of date seem to perform satisfactorily if they were frozen, can one assume that this effect would be neglibible except in the most critical of applications?
 

leo_jar

Member
True is that the best status (color balance /contrast) of consumer film is one year to one and the half year after manufacturing depends on the storage condition. Kodak formulates the consumer film according to the customer behaviour and storage condition. However, you won't know when the film is the best since you has no idea about the previous storage condition of the film. Professional film is made for immidiate use after leaving the frige.

Gamma radiation does affect the film especially the high speed film. Generally, it doesn't has significant effect on normal speed film even you store them in frige for years.

Kodak do have a mile deep salt mine for storing the scientific and control film.
 
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