MicrofilmIn order to be kept for hundreds of years, microfilm must of course be permanent in itself but it must also be correctly exposed and processed.
The camera film is normally used for archival purposes and is kept in specially designed depositories with good storage conditions. The film copy to be read is normally of the third generation, made by copying from a master copy of the original.
Official authorities that intend to use microfilm for keeping of records shall prepare a test film that has to be tested by an accredited testing laboratory. The microfilms to be kept for the future shall be tested with respect to technical quality and residual processing chemicals by an accredited testing laboratory. SP is the only Swedish accredited laboratory for these tests.
The permanence of microfilm which is to be stored for a very long period of time, is tested in accordance with the Swedish National Archives Regulations. Microfilm may be certified, read more under link to the right "Certification of archival materials". SP is the only accredited certification body in Sweden.
You can find a list of microfilming companies that fulfils the Swedish requirements concerning microfilming of drawings in document "Mikrofilmframställare". (Can be downloaded to the right of this page.)
Residual processing chemicals
We perform analysis of processed microfilm with respect to residual processing chemicals. The amount of thiosulphate is determined with the Methylene Blue method in accordance with ISO 417 or with a method using silver nitrate, which may be used to detect also the degradation products of thiosulphate. The latter method has the advantage that it can be used to detect the position of the residuals on the film. It is thus a useful tool when trying to find the reason for incorrect processing.
This image shows samples from testing of resudual
processing chemicals. The samlple to the left comes
from a film that is free from thiosulphate. The right
sample comes from a film with more than 0,7ug
thiosulphate per cm2 of film.
The legibility is, of course, of primary interest in information storage. It is of special importance when data is stored in a way that special equipment has to be used for information retrieval. At SP, we have many years of experience of evaluation of the legibility of microfilm and the influence of the quality of the first generation on the technical quality of copies of later generations.