Cinematography and their materials
The audiovisual materials have cultural and artistical relevance as paintings, sculptures or historical building and, for this reason, they are considered cultural goods that must be preserved and, where needed, restored. Do you know what they really are? What is the material (or the materials) composing the analog medium on which images are imprinted and transformed into photographs or movies? So, what are photographic and cinematographic films?
Basically, modern films used until the digital Era were long polyester strips (PET) with perforations on both sides, coated with several layers of gelatine emulsion and light-sensitive microparticles. The so prepared filmstrip was ready to be imprinted with still images (the frames) by means of light. After that, the audio track (a continuous wavy line, from the top to the bottom of the strip) was added on the film itself. Thanks to the PET property, the filmstrip was flexible as well as traction and fire resistant.
However, the cinematographic film has undergone various evolutions and improvements in its history, before arriving to the PET stable version we are familiar with. At the end of the 19th Century George Eastman, founder of the historical Kodak Company, invented and sold a celluloid film base coated with gelatine emulsion containing silver halide crystals. This preparation was similar to the first coating used to imprint photographic images on metal plates, combining silver nitrate (AgNO3) and silver halides, that is, light-sensitive crystals with animal gelatine. An external protective layer, an anti-halation layer and additional adhesive layers besides the base and emulsion, were part of stratigraphy of the analog picture medium.
Unfortunately, the film base prepared in this way was highly unstable and inflammable (have you ever seen the Italian movie "Nuovo Cinema Paradiso" by Giuseppe Tornatore?). In addition, with aging the gelatine decays and the celluloid becomes brittle, splitting in flakes, especially when films are rolled and stored in cans.
To solve this problems, different type of film base with better properties were developed, in both cinematographic and photographic fields. In 1930s the cellulose triacetate substituted the celluloid base and the use of acetic acid and acetic anhydride in presence of sulfuric acid as catalyst substituted the cellulose nitration process. The triacetate film was largely used from the 1950s to the ‘90s, when this material was replaced by the PET strips.
What about the pictures? Movies were born with black and white images, because the film stocks were low sensitive to the light: indeed, if a part of the film gets in touch with the light, it becomes darker (producing the negative). Nevertheless, the first films were covered with an emulsion sensitive to blue-violet wavelength, producing the medium images in few shades of the grey scale and not many details. At the beginnings of the 20th Century, new emulsions were developed and the so-called “panchromatic film” was born: it was sensitive to all the wavelengths of the light, allowing to realize pictures with much more shades of grey (more than the famous 50!) and a better image resolution. In 1936, the Kodak Company invented the “Kodachrome”, that was a film able to return colour and positive images, avoiding the use of the negative.
Together with the use of new media, several kind of video formats were invented, as the 35mm film (still used and considered as a standard), the Super8 film or the IMAX (Image MAXimum), that is one of the last formats produced and used in the movie theatres.
However, the cinematographic film has undergone various evolutions and improvements in its history, before arriving to the PET stable version we are familiar with. At the end of the 19th Century George Eastman, founder of the historical Kodak Company, invented and sold a celluloid film base coated with gelatine emulsion containing silver halide crystals. This preparation was similar to the first coating used to imprint photographic images on metal plates, combining silver nitrate (AgNO3) and silver halides, that is, light-sensitive crystals with animal gelatine. An external protective layer, an anti-halation layer and additional adhesive layers besides the base and emulsion, were part of stratigraphy of the analog picture medium.
Unfortunately, the film base prepared in this way was highly unstable and inflammable (have you ever seen the Italian movie "Nuovo Cinema Paradiso" by Giuseppe Tornatore?). In addition, with aging the gelatine decays and the celluloid becomes brittle, splitting in flakes, especially when films are rolled and stored in cans.
To solve this problems, different type of film base with better properties were developed, in both cinematographic and photographic fields. In 1930s the cellulose triacetate substituted the celluloid base and the use of acetic acid and acetic anhydride in presence of sulfuric acid as catalyst substituted the cellulose nitration process. The triacetate film was largely used from the 1950s to the ‘90s, when this material was replaced by the PET strips.
What about the pictures? Movies were born with black and white images, because the film stocks were low sensitive to the light: indeed, if a part of the film gets in touch with the light, it becomes darker (producing the negative). Nevertheless, the first films were covered with an emulsion sensitive to blue-violet wavelength, producing the medium images in few shades of the grey scale and not many details. At the beginnings of the 20th Century, new emulsions were developed and the so-called “panchromatic film” was born: it was sensitive to all the wavelengths of the light, allowing to realize pictures with much more shades of grey (more than the famous 50!) and a better image resolution. In 1936, the Kodak Company invented the “Kodachrome”, that was a film able to return colour and positive images, avoiding the use of the negative.
Together with the use of new media, several kind of video formats were invented, as the 35mm film (still used and considered as a standard), the Super8 film or the IMAX (Image MAXimum), that is one of the last formats produced and used in the movie theatres.
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