Methylene
Blue Test
Gosford
Micrographics are the only commercial microfilm service centre, in
Australia, that still conducts methylene blue tests on a regular basis,
at their facility.
One of the most common methods of testing for residual (left over)
chemicals on microfilm is the methylene blue test. This is conducted
according to
the following standard:
- ISO
18917 1999 Photography – determination of residual thiosulfate and
other related chemicals in processed photographic materials – methods
using iodine-amylose methylene blue and silver sulfide.
Testing chemical
levels
The processed silver halide
microfilm must be tested to make sure that
he chemicals used in developing and fixing the images have been removed
from the film by proper washing. If these chemicals remain on the film,
they will cause the images to fade and discolour in the longer term.
Testing process
- This
test measures the levels of residual thiosulfate in the processed film.
The maximum permissible concentration of thiosulfate is 1.4 micrograms
per square centimetre - this is often written as 1.4 µg/cm2
(where µg = micrograms)
- The test is done on a portion of the processed film taken from
the trailer.
- The test must be completed within 14 days of the camera master
film being processed.
- The operator must handle the test film carefully at all times
with clean white cotton gloves to prevent contamination.
- The operator must individually identify test samples (eg
title/date). This will assist in following up any processing problems.
- Any failure will require all film processed with that batch to be
rewashed.
- Certification of testing - the testing organisation must give a
written report confirming the test results.
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