Instant film
Instant film is a type of photographic film that was introduced by Polaroid Corporation to produce a visible image within minutes or seconds of the photograph's exposure. The film contains the chemicals needed for developing and fixing the photograph, and the camera exposes and initiates the developing process after a photo has been taken.
In earlier Polaroid instant cameras the film is pulled through rollers, breaking open a pod containing a reagent that is spread between the exposed negative and receiving positive sheet. This film sandwich develops for some time after which the positive sheet is peeled away from the negative to reveal the developed photo. In 1972, Polaroid introduced integral film, which incorporated timing and receiving layers to automatically develop and fix the photo without any intervention from the photographer.
Instant film has been available in sizes from up to size, with the most popular film sizes for consumer snapshots being approximately . Early instant film was distributed on rolls, but later and current films are supplied in packs of 8 or 10 sheets, and single sheet films for use in large format cameras with a compatible back.
Though the quality of integral instant film is not as high as conventional film, peel apart black and white film approached the quality of traditional film types. Instant film was used where it was undesirable to have to wait for a roll of conventional film to be finished and processed, e.g., documenting evidence in law enforcement, in health care and scientific applications, and producing photographs for passports and other identity documents, or simply for snapshots to be seen immediately. Some photographers use instant film for test shots, to see how a subject or setup looks before using conventional film for the final exposure. Instant film is also used by artists to achieve effects that are impossible to accomplish with traditional photography, by manipulating the emulsion during the developing process, or separating the image emulsion from the film base. Instant film has been supplanted for most purposes by digital photography, which allows the result to be viewed immediately on a display screen or printed with dye sublimation, inkjet, or laser home or professional printers.
Instant film is notable for having had a wider range of film speeds available than other negative films of the same era, having been produced in ISO 40 to ISO 20,000. Current instant film formats typically have an ISO between 100 and 1000.
Two companies currently manufacture instant film for Polaroid cameras: Polaroid for older Polaroid cameras and its I-Type cameras, and Supersense that manufacture pack film for Polaroid cameras under the One Instant brand.
How it works
Instant positive film uses diffusion transfer to move the dyes from the negative to the positive via a reagent. The process varies according to the film type.Roll/pack film
In 1947 Edwin H. Land introduced the Polaroid-Land process. The first instant films produced sepia tone photos. A negative sheet is exposed inside the camera, then lined up with a positive sheet and squeezed through a set of rollers which spread a reagent between the two layers, creating a developing film "sandwich". The negative develops quickly, after which some of the unexposed silver halide grains are solubilized by the reagent and transferred by diffusion from the negative to the positive. After a minute, depending on film type and ambient temperature, the negative is peeled away to reveal the picture which was transferred to the positive receiving sheet. True black and white films were released in 1950 after problems with chemistry stabilization were overcome.The reagent was contained in a pod, which would be pressed and eventually broken by the rollers that would then spread the reagent across the film. The reagent contained a solvent for silver halide such as sodium thiosulfate, for example.
With that being said, photographers and enthusiasts still practice with this limited, special and discontinued film, with both older Polaroid stocks or Fujifilm FP-100C or FP-3000B varieties. Multiple companies made film backs that would adapt camera to use this film with a specific detachable back.
Subtractive color films
Color film is much more complex due to multiple layers of emulsion and dye. The negative consists of three emulsion layers sensitive to the primary colors each with a layer of developing dye beneath it of the complementary color. Once light exposed the negative, the reagent is spread between the negative and positive and the developing dye layer migrates though diffusion to the positive surface where it forms the photo. Emulsion layers exposed to their respective color block the complementary dye below it, reproducing the original color. For example, a photo of a blue sky would expose the blue emulsion, blocking all the yellow dye beneath it and allowing the magenta and cyan dye layers to migrate to the positive to form blue.Integral film
This process is similar to subtractive color instant film with added timing and receiving layers. Land's solution was to incorporate an opacifier, which would darken when ejected from the camera, and then become clear to reveal the photograph. The film itself integrates all the layers to expose, develop, and fix the photo into a plastic envelope and frame commonly associated with a Polaroid photo.There are two kinds of integral instant photographic film: one where the side that is exposed to light, is opposite to that used to view the photograph, developed by Kodak, and another where the same side is used for exposing the photograph and viewing it, developed by Polaroid for the SX-70 camera. Again to develop the film a pod with a reagent on one side of the film is broken and the contents are spread within the integral film.
For films with the same view/expose side the reagent had white pigment, opacifying dyes, potassium hydroxide, and a thickener, which would be spread on top of a stack of cyan dye developer, red-sensitive silver halide emulsion, an interlayer, magenta dye developer, green-sensitive silver halide emulsion, an interlayer, a yellow dye developer, a blue-sensitive silver halide emulsion, and an anti-abrasive layer. This stack would be on top of an opaque polyester back. Above the reagent would be an image-receiving mordant layer, a timing layer, an acid polymer and a clear polyester layer. The pigment would be white titania in a suspension, and the opacifying dyes would be opaque at high pH levels but mostly transparent at low pH levels. The developers would contain metals such as copper for cyan, and chromium for magenta and yellow. These would form metal-containing dyes, with better lightfastness. Eventually this type of film from Polaroid received a silver-ion catalyzed process for dye release for the magenta and yellow dye layers.
Instant films with different view and expose sides had, as seen from the view side, from the front towards the back of the film, in layers: A backing layer, a clear polyester layer, a mordant to receive the image in the film, a titanium white light reflecting layer, a carbon black opaque layer, a releaser for the cyan dye, an emulsion sensitive to red for film reversal and a nucleating agent, an oxidized developer scavenger, a releaser for the magenta dye, an emulsion sensitive to green for film reversal and a nucleating agent, another oxidized developer scavenger, a releaser for the yellow dye, an with emulsion sensitive to blue for film reversal and a nucleating agent, a UV absorbing topcoat, a mixture of processing reagents such as potassium hydroxide, a film developer, carbon, a thickener, antifoggant and sulfite, two timing layers, an acid polymer, a clear polyester layer and a backing layer facing the expose side of the film.
The reagent is highly alkaline and when spread across the stack, it solubilizes or dissolves and moves the chemicals in the stack, which starts the photographic developing process. The silver halide that is exposed to light undergoes redox reactions with developer, and leaves free, undeveloped silver halide with silver ions that can modify image-forming dyes. The solubility and thus diffusivity of the dyes changes locally according to the local levels of these silver ions and in turn controls the amounts of dye that can diffuse to the image-receiving layer, and in which places.
The dyes then diffuse through the stack and the reagent, driven by electrostatic and chemical gradients, and deposit into the image-receiving layer. The reagent is what allows the dyes to move up the stack via diffusion. Dye release frees dye molecules to move up the stack via diffusion into the image-receiving layer.
Additive color film
Additive film uses a color mask of microscopically thin transparent red, green, and blue lines and a black and white emulsion layer to reproduce color images in transparency film. The resulting dye developers block the colors not needed and project the color or combination of colors which form in the resulting image. Since the lines are so close to each other, the human eye easily blended the primary colors together to form the correct color, much like an LCD display or television. For instance, a photo of a yellow flower would expose the emulsion beneath the red and green masks and not the blue mask. The developing process removed the exposed emulsion and diffused the unexposed dye developer to its receiving layer, blocking light from coming through. This resulted in the projected light shining through the red and green masks but not the blue mask, creating the color yellow. Because of the film density, film speeds were necessarily slow. High precision was required for the production of this film.Film brands
Polaroid
invented and produced the widest range of instant film. Roll film was distributed in two separate negative and positive rolls and developed inside the camera. It was introduced in 1948 and was manufactured until 1992. Sheet film was introduced in 1958 for 4x5" film holder #500. Each sheet contains a reagent pod, negative and receiving positive, and was loaded separately and developed outside the film holder. In 1973 Polaroid introduced 8x10" Instant film. Pack film was distributed in a film pack which contained both negative and positive sheets and was developed outside the camera. It was introduced in 1963. Integral film is also distributed in a film pack, but each film envelope contains all the chemical layers to expose, develop, and fix the photo. It was introduced in 1972.Polavision was an instant motion picture film. Polavision was introduced by Polaroid in 1978, with an image format similar to Super 8 mm film, and based on an additive color process. Polavision required a specific camera and tabletop viewer, and was not a commercial success, but did lead to the development of an instant 35 mm color slide film. Polachrome was an easy to develop 35 mm film, available in color, monochrome and 'blue' formats. Each roll of film came with a cartridge containing developing chemicals which were pressed between the film and a developing strip by a hand-cranked machine called the AutoProcessor. The AutoProcessor was very cheap and did not require a darkroom; the results were somewhat variable, the resolution was not as good as conventional film due to the matrix of tiny red, green and blue filters required to make the monochrome emulsion work in color, and the sensitivity was low, even for slide film; in tungsten light, Polachrome CS is rated at ISO 40. It was introduced in 1983.
Polaroid integral film packs usually contain a flat "Polapulse" electrical battery, which powers systems in the camera, including exposure and focusing mechanisms, electronic flash, and a film ejection motor. The inclusion of the battery within the film pack ensures that a fresh battery is available with each new pack of film.