What is photographic film made from?
Film is composed by two main parts, the base and the emulsion.
The base is where the emulsion lies. Usually it’s made of cellulose triacetate, acetate, or polyester. It’s a synthetic support that holds the emulsion.
It’s designed to endure winding and re-winding in the camera, so the most important characteristic is its ability to stretch, while maintaining a clean and uniform transparency. It must be resistant to scratches (as much as possible, camera functionality matters) and protect the emulsion, while also allowing the emulsion to be active.
Most film bases are made from plastic pellets that are melted and then stretched to a flat surface and cooled until the desired final size is reached.
The emulsion is the active ingredient that will capture the final image. When at its solid sate the emulsion consists of light-sensitive particles dispersed onto a gelatin support, and then coated on the base.
Built up from multiple layers of dyed silver halides, the emulsion, when hit by light, will transform into a latent image. Each layer will capture the correct corresponding wavelengths of the color spectrum.
Other important layers that are part of the film composition are positioned at the top, in between, and at the bottom, to control UV light, and anti-halation.
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What is the difference between panchromatic and orthochromatic film?
Orthochromatic film is made with blue-sensitive silver halide crystals, while panchromatic film adds other chemicals to increase the film’s sensitivity into the green and red parts of the spectrum.
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How many layers does a film emulsion have?
There are several layers in a film emulsion and their characteristics vary with each manufacturer.
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How is the emulsion coating applied to the film?
The coating of a film is a layer of emulsion containing microscopic light-sensitive silver halide crystals.
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What are Silver halide crystals?
A silver halide is a chemical compound that forms between the element silver and one of the halogens. When the crystals are exposed to light they react and form latent images.
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How does film work?
A photograph is the final result that occurs when a chemical reaction exists between light and sensitive silver grain compounds.