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Subject: Bentonite


From: Petra Nirmaier <petra.nirmaier<-a>
Date: Tuesday, August 12, 2008
Ruhi Baharad <conschem [at] imj__org__il> writes

>We have began testing bentonite/montmorillonite (Wisepac, Desi Pak,
>Wisesorb) to reduce relative humidity in display cases at the Israel
>Museum in Jerusalem. ...

We have 3 cases displaying archaeological iron objects in 2
different museums. The manufacturer of the display cases is for all
3 the same, but only one works effectively. The others haven't been
produced according to our specifications, so they aren't really
airtight. I will give you the measures  only for the one display
case that works properly.

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

 We achieved 5% RH.

>    How long did the RH remain constant in the vitrine?

It didn't exceed 10% RH within one year.

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

We add a simple hair hygrometer and for  extra control a RH
indicator strip with a colour change at 8%.  A datalogger would be
best, of course.

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

We have had the display case working properly for more than 4 years.

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

So far the DesiPak could easily be regenerated and also the bags
didn't suffer.

>    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?

I dry them at around 120 deg. C in a ventilated oven and it takes
around 3-4 hours.  I turn them over once and check if they are dry
by placing them on a mirror or shiny metal plate to see if there is
still condensation.

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

I  guess I also have the Tyvek bags. Regeneration with loose
material  is certainly much faster, but the bags are very convenient
to handle.

>    What is the formula to calculate the amount needed per cubic
>    meter?

I think it all depends on the degree of airtightness of your case,
as I have experienced with the 2 cases that aren't.

In the display case that works properly, we have 6 kg DesiPak in a
volume of 0,3 m3. For more information about calculating the amount
needed, see <URL:>

Petra Nirmaier
+41 41 228 71 70

                  Conservation DistList Instance 22:10
                 Distributed: Thursday, August 14, 2008
                       Message Id: cdl-22-10-003
Received on Tuesday, 12 August, 2008

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