Film base

Film base is the material that film emulsion is printed on. You may need to handle prints differently in exhibition settings depending on the material their base is made of.

Polyester stock

With rare exceptions, all 35mm release prints made since the late 1990s have been printed on polyester base. Many 16mm prints from the mid 80s onward are also printed on polyester stock. Nothing pre-1955 will be on polyester base. Unlike acetate or nitrate stock, polyester is essentially unbreakable and cannot be torn by human hands. It is also not susceptible to vinegar syndrome and does not warp or shrink (though it is not uncommon for the film to have a slight "bow"). It is believed that a film printed on polyester stock will last several hundred years because the base does not deteriorate [cite]. Polyester base is easy to identify because it is slightly thinner than acetate or nitrate, which also means adjustments in focus must be made if acetate and polyester films are spliced together in a single reel (such as a trailer reel). Polyester film cannot be cement spliced - it must be tape spliced or ultrasonic spliced.

• Polyester stock is often referred to as "Estar base" which is the Kodak trade name for their polyester stock.
• A guide for making a film viewer for easy identification of acetate or polyester film base. Older polarized 3D glasses (they use spherical polarization) work great for this if you can find some. Real-D glasses do NOT work. Polyester base will create a sort of "rainbow" effect when viewed between the cross polarized lenses, acetate base will not.

Acetate base

"Used in the early 1930s mostly for small gauges, then was widely used post 1950s to replace nitrate base. Often refered to as "safety film". Acetate" base in modern exhibition settings usually refers to triacetate base. Diacetate was used on some early safety film, but you won't see it very often under normal circumstances (whatever THOSE are!). Older acetate prints tend to be more brittle and prone to warping as they lose moisture. Acetate is thicker and tends to break when stressed. Use only tape or cement splices.

* Acetate base prints can suffer from vinegar syndrome if not stored at the proper temperature and humidity levels. Make sure they are kept cool and dry, and separate out any prints you suspect of having vinegar syndrome (even the beginning stages) as it can spread from one print to another.

Nitrate

Nitrate base is the infamously unstable and flammable stock that most release prints were made of until the early 1950s. Discontinued in 1951 and replaced with acetate "safety film". Look for the word "nitrate" written on the side of the film, though make sure it's not printed in from the original negative, as many nitrate prints were later re-struck on acetate or polyester stock. It's considered a hazardous material and becomes more dangerous as it deteriorates. Make sure you know the proper storage specifications for nitrate if you have any!

Resources

• Film Forever: Film Stocks and tips on home storage
• Historical Film Colors
• Make your own film base viewer
• Testing for vinegar syndrome