INTRODUCTION TO IOWA'S CENSUS
IOWA'S FEDERAL CENSUS YEARS
IOWA'S TERRITORIAL AND STATE CENSUS YEARS
WHERE TO FIND THE FEDERAL CENSUS MICROFILMS
WHERE TO FIND THE STATE CENSUS MICROFILMS
RESEARCH/DATA TRANSCRIPTION TOOLS
IOWA FEDERAL CENSUS PROJECT
IOWA STATE CENSUS PROJECT
OTHER HELPFUL WEBSITES
Microfilm Basic Technical Information
Silver Halide Film
- 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 in the original image.
- Silver Halide is the only film that is considered archival.
- Silver-halide print films are of two types: Polarity reversing and direct-duplicating.
- Silver-halide film should not be stored with other kinds of film.
- Best film type for census records.
- The Diazo process is used exclusively for making copies of the master film. It is not sensitive enough to be used as a camera negative film. The process has been used since the 1920's.
- Diazo is a polarity maintaining copy. (i.e. negative to negative.)
- Do not use in strong sunlight. Sunlight contains ultraviolet light and will ruin the film even after processing.
- Vesicular films became popular not only because of the ability to reverse the image but also because it can be handled in daylight and process using a dry thermal process. The image is comparable to silver when projected on a reader screen.
- Image reversing
- Can be handled in daylight.
- Best film type for newspapers.
Reprint Permission granted September 25, 1997 by:
Reference: Manual of Archival Reprography 1989
Heritage Microfilm, Incorporated
1450 Boyson Road, Building B
Hiawatha, Iowa 52233