█ AGNIESZKA LICHANSKA
Microfilms are miniature films used for photographing objects and documents. The images on these films cannot be seen without an optical aid, either in the form of a magnifying glass or a projector. The main advantages of microfilm include relatively low cost, good image quality, long life and lack of necessity for expensive viewing hardware. Although the images are not visible with a naked eye, only a magnifying glass is needed for reading the microfilms.
Technology behind microfilms. The first mini-photographs (8x11mm) were taken using a portable Daguerrean camera produced in 1839. Much later, during the Cold War, the mini-photographs were developed into microdots, tiny photographs of 1mm or less in diameter, looking like a period in a typewritten letter.
The microfilm itself was invented in 1839 by John Dancer. He replaced a slide on the microscope stage with a photographic film and reversed the normal process of microscopy. As a result, instead of seeing a large version of a biological specimen, he was able to produce a miniature image of a large object.
Early microfilms were based on cellulose acetate and over the decades they broke down into acetic acid (vinegar syndrome) and records were destroyed. Currently, there are three types of microfilm: silver halide, diazo, and vesicular. Silver halide films are similar to the traditional film. They consist of the polyester base and silver nitrate emulsion, and are used in cameras for producing the original microfilms. Silver halide films produce the highest resolution and are available as positive and negative image films. If properly stored, their life is estimated to be at least 500 years. Diazo and vesicular films are less stable. Images on diazo films are formed from diazonium salts exposed to ultraviolet light in the presence of ammonium; these images fade with time. The vesicular films produce images by little bubbles inside the film that are sensitive to pressure and can also be destroyed by heat.
Not only did the films (down to 8mm wide) and images become smaller, but cameras were reduced in size and often disguised as everyday items such as watches, cigarette packs, books, and matchboxes. In fact, Kodak produced a camera known as Camera X or Matchbox camera. This camera was used during the Second World War by allied resistance groups. A second camera that was developed just before the war was the Riga Minox camera designed by Walter Zapp in 1936. Initially the minicameras were marketed for the public, but they were very quickly adopted for espionage purposes by intelligence and government agencies.
Microfilms in espionage. Microfilms were first used for espionage in 1859, and were later used to transport messages during the Franco-Prussian war of 1870 by carrier pigeon. However, they came to much more prominence in the 1920s for keeping copies of bank records and development of Recordak by Kodak. It was, however, during the Second World War when the microfilms flourished. They were used in regular military mail by the American forces to reduce the cost of shipping tons of mail. Microfilms were also the main way to photograph military installations and documents, as well as types and rates of weapons production. They were also used to transfer coded messages between the army and the intelligence agents behind enemy lines. Transport of the microfilms was not difficult due to their small size. Microfilms were, and still are, easily concealed in hollowed-out pencils, pens, cans, coins or other instruments smuggled by couriers across borders, and in many cases they remain a method of choice for espionage.
Microdots can be concealed even more easily than microfilms by being placed in a regular letter, under a stamp or in a dental filling. Microdots have also become
an anti-theft device: a Stop theft microdot can be used to mark property.
█ FURTHER READING:
Pritchard, Michael, and Douglas St. Denny. Spy Camera: A Century of Detective and Subminiature Cameras. London: Classic Collections, 1993.
White, William. The Microdot: History and Application. Williamstown: Phillips Publications, 1992.
Minoxography Community. D. Scott Young and Ferry Ansgar. "A Brief History of Minox." <http://www.minoxography.org/history.html> (10 March 2003).
University of California. Southern Regional Library Facility. The history of microfilm: 1839 to present. December 3, 2002. <http://www.srlf.ucla.edu/exhibit/text/BriefHistory.htm> (10 March 2003).
DNA Sequences, Unique Photographic Resolution Rosenberg (Ethel and Julius) Espionage Case