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What is film made of

Animal, vegetable and mineral

When film was invented it was made from cellulose nitrate, but modern day film is made either from a cellulose acetate or polyester base with a coating of light sensitive minerals of silver salts. In colour films the light activated emulsion is laid onto the base in three layers each containing colour dyes

• Magenta
• Yellow  
• Cyan    

The medium used to bind the emulsion is made of gelatine, a natural polymer from animal bones and hides.

• Minerals in the form of salts
• Animal in the form of gelatine
• Vegetable, polyester is made from petroleum, which is basically decomposed vegetable matter

We've all heard film referred to as celluloid, a popular term for cellulose nitrate, Mainly cellulose acetate is used to make film bases. However, due to its durability and stability, polyester has become more widely used for distribution prints and other films that will not need to be edited or permanently spliced together.

Cellulose acetate is formed from plant material ,The cellulose in cellulose acetate is either wood pulp or short cotton fibres. These are natural polymers. Films made of acetate are still common because they can be fused together in the editing process.

Acetate vs. Polyester

Each type of film base has its advantages and drawbacks. And each, as well, has its appropriate uses.

Polyester film is stronger, more resistant to tearing, and less brittle and can therefore be made thinner and lighter than acetate. It is also more durable and resistant to degradation or decay. This strength and durability makes it great for distribution prints in the cinemas.

However, polyester film is often so thin that it can create difficulties with older projection and processing equipment which does not have the kinds of tolerances required for the newer thinner films. It can also get tangled up in the film path or wander from the film path in self threading machines. It also cannot be spliced together with a solvent the way acetate film can. Splicing polyester film together requires a heat fusion process which does not lend itself to editing.

And the refractive qualities of polyester base are greater than those of acetate, sometimes causing halo's of light around bright areas in the image. To prevent this manufacturers have added a thin grey layer in the film, between the emulsion and the base to dim the light as it reaches the clear base material.

The two films are found to be equally resistant to scratches and general wear. And each type of film serves it's assigned purpose well. Libraries, distributors and amateurs can benefit from the strength of polyester, while editors and filmmakers can work easily with the more traditional acetate stocks.