SHOOTING EXPIRED FILM
Buying expired film on ebay is very tempting as it's cheap and in abundance. We recommend shooting expired film if you're wanting to test some ideas out with cheaper film or if you are looking for that mega grainy quality. But not many people know that expired film that is at least 5 years out of date needs to be rated at a different ISO than its original box speed. This is to combat its age - film isn't as sensitive to light due to the climate it has been kept in. If it is in a humid or damp place, it will deteriorate quicker, causing the colours of the film dyes to shift in colour film and increased grain. If you buy the film fresh, make sure to store it in a fridge or freezer to maintain its lifespan.
Here is a basic guide on how to re-rate your film depending on the number of years it has been expired for: