Waterlogged lignite

On behalf of Cedric Andre, Kim Travis <kim.travis [at] slm__admin__ch>
writes

>Has anyone experience in the drying treatment of waterlogged
>lignite? This small artefact, a fragment of a decorated arm bracelet
>and ca. 4 cm. in length, was excavated recently from a waterlogged
>freshwater site in an urban environment of Switzerland.  The two
>known experiences we have of treatment for this type of material are
>(1) slow air drying and (2) controlled air drying after impregnation
>with a mixture of PEG 400 and PEG 1000. Any words of advice would be
>appreciated,

In Instance 18:16, Kim Travis asks for information about treating
waterlogged lignite.  In my previous job at English Heritage I
successfully treated a large number of waterlogged Roman shale (or
lignite) bracelet fragments using PEG.  The fragments were immersed
in a 10% w/w solution of PEG 4000 in a glass beaker covered with
cling film.  The beakers were placed in an oven at approx 60 deg C
and the water was allowed to evaporate slowly, over a period of
several weeks.  The PEG diffused into the shale, and eventually the
fragments were left immersed in pure molten PEG.  (PEG 4000 has a
melting point of about 55 deg.)  The fragments were then removed,
wiped with paper tissues to remove excess PEG, and left to cool.
The PEG acts as a consolidant and adhesive to hold the pieces
together, as shale tends to delaminate, particularly if allowed to
air-dry.  After treatment the fragments appear black with a slight
shine, but not waxy-looking. Breaks and delamination can be fixed
using molten PEG and a hot air blower.

Dr Barry Knight
Head of Conservation Research
The British Library
96 Euston Road
London NW1 2DB
+44 20 7412 7229
Fax: +44 20 7412 7658


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                  Conservation DistList Instance 18:17
                 Distributed: Thursday, October 7, 2004
                       Message Id: cdl-18-17-003
                                  ***