Consolidating mica

Laurent Sozzani <l.sozzani [at] rijksmuseum__nl> writes

>I am looking for information on the consolidation of thin sheets of
>splitting mica.  We have a set of costume overlays painted on mica
>that are laid over a small miniature portrait painted on copper.
>Handling has damaged some of the mica overlays--should they be
>consolidated?  Is it desirable to consolidate the mica as opposed to
>letting well enough alone and relying on good storage and minimal
>handling for their preservation.

In limited experience curating geological specimens, I have found
that most micas enjoy considerable toughness within sheets and
respond well to plastics and consolidants between sheets.  Presuming
each layer of your overlays is composed of multiply splitting
sheets, you may well be able to glue the leaves together to prevent
any further degradation. You are likely working with muscovite,
which is generally prone to scratching on cleavage surfaces but
mostly impervious to acid/chemical degradation [may etch slightly in
stronger acids].  I have had success with Butvar and even CA glue
under vacuum, but cannot attest to long term effects or stability.
Another common solution is optically neutral microscope mount epoxy,
such as Petropoxy, which will be effectively irreversible and will
stiffen flexible sheets.

Alternatively, if you are photographing or storing, you might
impregnate the mica sheets with optical oils, optionally  sealing or
clamping the edge, to achieve transparency; you can match the index
of refraction in this way, restoring the sheets to their original
optical properties in this way.  Viscous oil tends to promote
adhesion between cleavage surfaces and will therefore stabilize your
sheets [or 'books'] without stiffening.

Jeff Bartlett
Coordinator
InsideWood Database
North Carolina State University


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                  Conservation DistList Instance 18:39
                 Distributed: Friday, February 18, 2005
                       Message Id: cdl-18-39-005
                                  ***