Storage of glass negatives

Rob Heesterbeek <rheesterbeek [at] museon__nl> writes

>These are the advised values for temperature and RH for storage of
>glass plate negatives that I found in literature, but I was
>wondering which one is the correct one? It is confusing.
>
>            Temperature in degrees Celsius      RH in %
>
>    ANSI                                20 - 50     15 - 25
>...

Please note that the ANSI (and ISO) standard which you have cited
must be from an old version.  The standard was revised in 1996.
Previously it had not been revised in years and did not reflect more
recent research, by McCabe and McCormick-Goodhart, or the influence
of humidity on glass corrosion. The revised environmental conditions
reflect the fact that glass may deteriorate in humid conditions
above 40% and that historic photos may have stressed emulsion layers
with existing flaking etc., that would be exacerbated dangerously by
relative humidity levels below 30%.

Below are the current recommendations for the extended term (long
term) storage of photographic plates in the ANSI/ISO standard. Short
term storage condition (0-10 years keeping) allow conditions of
greater temperature and relative humidity variance, with short term
peaks in the range mentioned in the old standard; but I assume
you're interested in the long term keeping conditions for
permanence.  There is other helpful info in the standard and I would
encourage you to obtain a copy.  It is available from Global
Engineering.  I assume the ISO standard is available from ISO in
Geneva.  Please note that the allowable daily fluctuation is a for a
peak variance and not a routine fluctuation. However, plates stored
in paper envelopes and in boxes would rarely 'feel' a short term
variance of 5% (10% total).

Photographic Plates-ANSI/PIMA IT9.18-1996  (ISO 3897) (specifies a
maximum temperature with a setpoint RH within an allowable RH range
for that temperature).  No LE (life expectancy) has been designated,
but actual history with the materials suggests 100+ years for well
processed plates.

Black and White  Max Temp/ allowable RH range:

    18 deg. C  ( approximately 65 deg. F)
    30-40%
    Max daily fluctuation allowed: +2 deg. C
        (approximately 5 deg. F) +5%

Sarah Wagner
Photo Conservator
ANSI Imaging Technology Committee member
revision author/coordinator for IT9.18


                                  ***
                  Conservation DistList Instance 13:47
                  Distributed: Tuesday, March 14, 2000
                       Message Id: cdl-13-47-003
                                  ***