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Subject: Bentonite


From: Ruhi Baharad <conschem<-a>
Date: Sunday, July 20, 2008
We have began testing bentonite/montmorillonite (Wisepac, Desi Pak,
Wisesorb) to reduce relative humidity in display cases at the Israel
Museum in Jerusalem. Needless to say we are placing the material in
tight cases. One important thing we realized is that much less
material is needed to dry the case compared to the amount when using
silica gel. We are interested in getting input--positive and
negative--regarding the use of this material in reducing relative
humidity and would appreciate answers to the following questions:

    What level of relative humidity was achieved? Up to 15%, 20-30%?

    How long did the RH remain constant in the vitrine?

    What indicator was placed in the vitrine to show rising RH?

    How long has your institution been using this material? Years?
    Are you satisfied with the results over this time period?

    How many times can the material be regenerated/dried in the
    oven? How long can this material work after so many

    We received different information regarding the duration of time
    in the oven--one company said 4 hours in the oven at 120 deg. C,
    the other said 24 hours at the same temperature Any other input?

    The material comes either in Tyvek or cotton bags. Apparently
    regeneration in the cotton is better? We have only the Tyvek

    What is the formula to calculate the amount needed per cubic

We have not been able to receive a definite answer from the supplier
here in Israel regarding this.

Ms. Irit Lev Beyth
Senior Object Conservator
The Israel Museum, Jerusalem, Israel
+972 2 670 8817

                  Conservation DistList Instance 22:7
                   Distributed: Friday, July 25, 2008
                        Message Id: cdl-22-7-012
Received on Sunday, 20 July, 2008

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