The short answer...   Microfilm: A film bearing a photographic record on a reduced scale of printed or other graphic matter.   The long answer...   Microfilming, also called microphotography, consists in the reduction of images to such a small size that they cannot be read without optical assistance. This amazing photographic compression often results in a ninety-nine percent saving of space. The microfilming service is one of the most extensively used and common practices in modern reprographic science. The remarkable increase in microfilming activities is due to the recognition that a large portion of books, periodicals and newspapers are deteriorating because of the poor quality of paper and print. The use of microfilming for almost seventy years has provided an excellent reproduction method for recording photographic images of printed materials. Using modern film, advanced processing technology and climate-controlled storage vaults, Heritage Microfilm produces images that will last 500 years or longer, far longer than most paper stocks in use today.   Types of Microfilm   Silver Halide Film   Silver Halide film is similar to traditional photographic film that uses a silver emulsion on a polyester base. Silver Halide is the film type used in the camera to make the master film. Silver Halide is the most light sensitive of all the films used, hence it can record a greater variance of density and contrast present in the original material. Silver halide is the only film that is considered archival. Properly processed and stored it has a Life Expectancy (LE) of 500 years. Silver film gives the highest resolution, and is the choice where longevity and high quality are paramount. Silver Halide print films are of two types: Polarity Reversing - Produces a positive image. Direct Duplicating - Produces a negative image.   Vesicular Film   Vesicular film, so called because the image is actually formed by miniscule bubbles or "vesicles" inside the film body itself. Vesicular films became popular not only because of the ability to reverse the image but also because it can be handled in daylight and processed using a dry thermal process. The image it renders is comparable to silver when projected on a reader screen for microfilm produced according to ANSI/AIIM/RLG standards. Vesicular films cost less to produce and therefore less for users to purchase. Vesicular films have a blue color on the reel. Vesicular film is a good choice for high-use applications, such as popular titles in a University or other research library. Vesicular film key points: Image reversing - Produces a positive image. Can be handled in daylight.   Diazo Duplicating Film   Once a low-cost alternative to silver duplicate microfilm, Diazo film has fallen into disuse because of its short shelf life, and susceptibility to degradation from everyday light sources. Heritage does not use Diazo film, and recommends against using it.