Works on Paper in the Tropics

Since it seems quite impossible to use a completely sealed system in
this case (variations in air pressure might break the glass and
other reasons), You will have to do with a not completely sealed
one. This means that if You intend to keep a work of art dry in a
relatively wet surrounding as it usually is in the tropics and if
You use a system where continuously a tiny flow of wet air will leak
in, You will need regular maintenance. You have to get this extra
moisture out of Your frame, otherwise the RH inside will continuously
rise till equilibrium with the surrounding is reached. The amount of
buffering material such as Art-Sorb will only determine the time
needed for this.

To solve Your problem, I would advise to my customers in this case
to use a relatively high amount of buffering material to achieve
long maintenance intervals. The RH inside the frame should be
monitored by a small hygrometer like the ARTEN-thermohygrometer or
at least an indicator-strip which should be observable without
moving the frame. If the RH inside the frame seems to be too high at
a certain moment, the buffering material should stay in the frame,
but one or more small bags of dry silica gel or clay should be added.
The number and size of these bags should be calculated in order to
bring RH inside the frame back to the initial value. These bags
remain inside the frame till RH has reached a critical value again.
Then the used bags are exchanged against dry ones.

The fact that the buffering material (This can be Art-Sorb sheet or
cassettes or whatever) always remains inside the frame makes sure
that the decrease in RH caused by the dry bags of silica gel will be
a slow one. Bags of silica gel are available in all possible sizes
and are not costly at all. They can be regenerated a number of times
at 130 deg C.

So the best solution will be to have a fairly airtight frame with an
integrated hygrometer and an easily accessible opening through which
You can exchange the bags of silica gel (and the hygrometer for
calibration). In Germany there are two manufacturers of
picture-frames with ARTEN-hygrometers integrated:

    Hahn who is represented in the USA
    info [at] glasbau-hahn__de
and
    Reier
    Fax: +49 035 722 365 65

Christoph Waller
Conservator/restorer
Distributor for Art-Sorb, Ageless and other products for museum
showcases for Germany and Europe
Im Buckle 4
D-79288 Gottenheim
+49 7665 94 03 90
Fax: +49 7665 94 03 91

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                  Conservation DistList Instance 11:71
                 Distributed: Friday, February 20, 1998
                       Message Id: cdl-11-71-004
                                  ***