expired film notes
expired film
Film has an expiration date. Its a chemical product and eventually those chemicals lose their sensitivity to light or shift in odd ways and the film is "expired". The scarequotes are because you can still use it for photography there are just a few additional things to keep in mind.
Normally the silver halide crystals on the film itself get exposed to light, the photons interact with the crystal and leaves behind the silver to later be developed. However, over time the crystals can and will break down without any light exposure, but the result is the same the silver atom is left behind as if it were exposed to very low light. There are two causes; heat, and background radiation.
Due to chemistry reasons, heat can also activate the silver halides in the film stock. Not a lot, but enough that over time it will have an effect. Its recommended to keep undeveloped film in the fridge or freezer to give it a chance to last until expiration. At the minimum keep it stored under 68 degrees Fahrenheit. When taking it out of cold storage, let it reach room temperature over about an hour (or else the crystals wont be 'awake' to react well with light).
The second cause of film expiration is background radiation. This is the very low level dose that you get walking around on our mudball Earth. Background radiation is a really cool topic because essentially some of it comes from stars exploding many light years away. No really. Sometimes when a star dies it will explode in a nova and release many high energy particles out into space in every direction. Since we are in one of those directions, some of those particles make it all the way here and get absorbed by your skin. Anyway. Radiation will also cause some the crystals to activate. Which is why you should always handcheck your undeveloped film at the airport! They will either know what's up and be super nice and maybe ask you about your photography, or they won't give a fuck at all but still give you a handcheck1.
So what are these effects?
1. the iso will drop
Because theyre are less unactivated crystals to absorb light, the overall sensitivity of the film will go down. What you can do as a photographer, is give it more light to compensate. The general rule of thumb is 1 stop per decade past expiration. In my experience this works well but it is not often you can do a side by side comparison to verify with a specific stock. If the storage history of the film is unknown or dubious, start with one stop extra per ten years, and another half or full depending how lucky your feeling. It really is a guessing game sometimes. If the film has been frozen since 1980 (and you believe that) it could be reasonable to shoot it at box speed.
2. the whole thing could fog up
The second effect is fogging, sometimes called a base fog or haze. This is exactly what it sounds like, expired film often creates images that are foggy or have a light white haze over the whole thing. This is from the heat/radiation/time that has randomly activated the chemistry without light. Compensating with an extra stop per decade can sometimes remove or reduce this. Often though the fog can be removed in editing/printing with some additional contrast.
3. the colors may shift
Obviously this is for color film only while the others apply to both color and black and white. Because color film has multiple layers of halides bound to dyes there are multiple things that can go wrong when it expires!
The colors will shift and it may be impossible to white balance it 'correctly' in post. Usually the positives will have a green or magenta tint in all the colors that isnt very pleasant. Lightly expired (2 stops or less) can usually be recovered to look 'normal'. But sometimes its fun to just leave it!
So what do you do if you have some expired film?
just go for it
Negative film generally has a bit of latitude, meaning you can over or under expose the frame and still get a usable final image. Its not super critical to figure exactly how much to compensate with expired film. Just have fun with it, and keep expectations low.
All of this advice is for negative filmstocks. Slide film (or color positive) ages like milk2. If it was more than 10 years out of date I wouldnt pay for expired slide film. You're gonna have a bad time.
If the film is just a few months out of date, you probably wont even notice, go for box speed. 1-5 years with good storage, add a 1/2 stop. Remember that film is pretty robust, so being off on the exposeure by a stop could still get you a usable image (usable but may not be pretty).
storage is key
Any film not planned to use within 6 months -> freezer. The rest in the fridge. Its good practice to let it warm up before opening and using, it being cold will cause condensation and you'll get water all over the film. It's also important to freeze it in a ziploc bag or airtight container for the same reason. Frost can form in those delicate layers of chemistry and physically damage it.