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Subject: Silica gel

Silica gel

From: Christoph Waller <info<-a>
Date: Tuesday, June 10, 2008
>Does anyone know if silica gel with a blue indicator is on the
>market again? The cobalt chloride indicator type was withdrawn a
>number of years ago, being replaced by orange/green indicator.
>However I was recently supplied with a batch of blue silica gel and
>haven't had any response from the supplier when querying it. Any
information would be appreciated.

Conventional cobalt containing blue gel still exists on the market.
It is not forbidden within European Community countries but it is
subject to specific labelling regulations. However, since it is
being suspected of being carcinogenic it should be avoided wherever
possible.

Nowadays there are plenty of new, non-toxic indicating silica gels
with different colour shifts. We only stock indicating silica gels
changing from orange to colourless at the moment, with colour switch
at  5-9% RH or at 30-40% RH (this is the other important thing: the
RH at which the colour shift occurs!). See

    <URL:http://www.llfa.de>

A good selection can be seen at

    <URL:http://www.hobby-photo.de/shop/pi2/pi3/index.html>

but there are many others, e.g.

    <URL:http://www.levosil.com>
    <URL:http://www.zeochem.com>

Also, some new, cobalt-free gels turn from blue to red, like the
"neo-blue" made by

    <URL:http://www.kukdongchemical.com>

or the "blue silica gel DL" made by

    <URL:http://www.haiyangchem.com>

It is possible that the new blue gel you received is a cobalt-free
type as well. To test: cobalt containing blue gel will stay blue at
200 deg. C, the cobalt-free types won't--this might be an easy way
to test which kind of product you are dealing with.

Christoph Waller
Long Life for Art
Hauptstr. 47
D- 79356 Eichstetten
Germany
+49 7663 608 99 0
Fax: +49 7663 608 99 20


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                  Conservation DistList Instance 21:65
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Received on Tuesday, 10 June, 2008

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