Magnesium carbonate as a fill material for marble

Kate Helwig <kate_helwig [at] pch__gc__ca> writes

>I am analyzing a repair (fill material) from a marble sculpture
>(believed to be sculpture grade Carrara marble). Analysis (by FTIR
>and XRD) showed the fill material to be composed of a hydrated
>magnesium carbonate with a smaller amount of quartz and probably
>sepiolite (a magnesium silicate). No organic binder was detected.
>I'm wondering if this could be a type of plaster fill based on
>magnesium carbonate rather than calcium carbonate.
>
>I have found reference to the presence of  magnesium carbonates in
>plasters where the lime comes from a magnesium-rich limestone,
>however I have not found any reference to plasters where hydrated
>magnesium carbonate is the major component. Has anyone come across
>this type of fill or a reference to the use of magnesium carbonate
>based plaster?

I have checked the "faker's handbook" (or "restorer's", dependent on
your ethics!), The Scientific American Cyclopedia of Formulas, Ed.
Albert A. Hopkins, Scientific American Publishing Co., New York
1932. On p. 301, right column, we find "Abolithe Cement" which
apparently fits Kate's description.

George Brock-Nannestad
Preservation Tactics, Denmark


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                  Conservation DistList Instance 15:62
                  Distributed: Tuesday, March 12, 2002
                       Message Id: cdl-15-62-005
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