preservation of lignite samples

[San Diego Natural History Museum]

A great deal of the answer to this depends on the chemical value of
the lignite and its included fossils, as consolidants will contaminate
future bio- and geochemical work. Many people are dividing such
collections and saving some part in isolation from both treatment and
environmental contamination.

Lignite is not very stable; I worked with some collections from central
Texas for several years. One of the best things you can do is to maintain
it in environmental conditions which are as stable and free from
fluctuation as possible. If there are a lot of various iron sulfide
compounds present, the relative humidity needs to be kept low: below 45%
if there are no problems already existing, below 30% if there is an
active reaction. If you have steel storage cases, it is possible to
modify them so that they maintain level RH inside, even if you cannot
provide it outside. You can also provide microenvironmental control
through the use of silica gel, but this requires much more silica gel
than is commonly used (or believed). Saturated salts can also be used;
consult a conservator for this.

Lignite will, as you know, not tolerate a lot of handling; this should be
minimized as much as possible. If you need to handle it and are not
worried about chemical contamination, you may want to try a consolidant
such as a polyvinyl acetate (e.g. Acryloid) or polyvinyl butyral (Butvar).
Steer clear of white glues, epoxies, and surface treatments.  You are
looking for something that is not often available off-the-shelf:
water-clear, low gloss, with no shrinking, embrittlement, or yellowing
with age. The most high-tech answer would be to use a vacuum-
polymerization treatment such as that used for preservation of the Axel
Heiberg Forest sub-fossil plant material, but that is probably outside
the budget and scope of most people, and it is completely irreversible
as well.

For more information on geological conservation, including a section on
conserving pyrite and its morph marcasite (pyrite is often found in lignite
and can be the source of oxidative breakdown), you might try _Conservation
of Geological Materials_ (ed,. Frank Howie) and _Conservation of
Paleontological Materials_ (ed. Chris Collins). Both are published by
Butterworths and have appeared very recently. For more information on
climate-controlled cases, please let me know off-list that you are
interested and I will send the references.

Shameless plug: I have worked with creating anoxic enclosures for
reactive pyrite, using oxygen-barrier heat-seal film and the iron oxide
oxygen scavenger Ageless, with great success. This might well work with
deteriorating lignite. The Society for the Preservation of Natural History
Collections will be issuing a technical leaflet on creating anoxic
enclosures, and International Academic Projects will be sponsoring a
course here in March on anoxic enclosures and other microenvironments.
Please let me know off-list if you would like more information on these.

Sally Shelton
Director, Collections Care and Conservation
Post-graduate diploma, Geological Conservation, Cambridge University

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|                                                                       |
|                 San Diego Natural History Museum                      |
|                          P. O. Box 1390                               |
|                San Diego, California   92112  USA                     |
|             phone (619) 232-3821; FAX (619) 232-0248                  |
|                     email LIBSDNHM at CLASS.ORG                          |
|                                                                       |
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On Thu, 21 Dec 1995, Jeremy Bruhl wrote:

> Hi
>
> I wonder whether anyone can provide advice on the best medium in which to
> place 'fresh' lignite samples in order to perserve and handle the material.
> The samples crumble and decay if exposed to the air. The samples are
> valuable, as they include plant macrofossils.
>
> Greetings.
>
> Jeremy
>
> =========================================
> Dr Jeremy J. Bruhl
> Department of Botany and New England Herbarium (NE)
> University of New England
> Armidale, NSW 2351
> AUSTRALIA
>
> Telephone: +61 67 73 2429
> Fax:          +61 67 73 3283
> Internet:      jbruhl at metz.une.edu.au
>