Collection Management:
Selection Based on Type of Film

Microform is made available from commercial micropublishes in a variety of film types, including: diazo, silver/silver-halide, and vesicular films. This document is intended to assist collection managers as they decide which type they might choose.

Vesicular film

• Vesicular film should be considered for the majority of titles.
• Resolution/image clarity of vesicular is not as good as silver-halide film.
• Vesicular has no emulsion layer and, therefore, is relatively impervious to scratches that obliterate the image.
• Vesicular is tolerant of high relative humidity.

Silver-halide

• Silver/silver-halide film should be considered when the title requires high resolution.
• Graphics with meaningful detail (i.e., aerial photography, satellite imagery, and art reproductions) and text (i.e., Burmese, Hebrew, etc. or pencil manuscripts) with fine lines require high resolution.
• Extremely fine grains of silver are used to make silver film. As a result of this refinement, silver film is capable of very high resolution and crisp, clear images.
• Silver is carried in a gelatin emulsion layer that is not tolerant of high relative humidity and only moderately tolerant of moderate relative humidity.
• Silver film is particularly susceptible to scratching. Because the emulsion, which carries the image, is a surface layer, scratches may obliterate the image.

Diazo film

• Diazo film should be considered with reservation and purchased only when neither vesicular or silver-halide films are available.
• Diazo film shares the poor qualities of both silver and vesicular film without a significant number of their benefits.
• Resolution/image clarity of diazo is not as good as silver or vesicular.
• Diazonium salts are carried in a gelatin emulsion layer that is not tolerant of moderate to high relative humidity.
• Diazo films may off-gas and released gases may be detrimental silver microfilm

Microform Collections & Relative Humidity

Without precisely defining levels of humidity for each microform collection location, it is sufficient to say that all have moderate to high relative humidity.