Mold on stone

Shelley Reisman Paine <shelley [at] srpaine__com> writes

>I am working on a set of oversize outdoor sculpture made from
>Carrara marble.  The sculpture stood outdoors for sixty years. After
>it was vandalized in 2000 the owner stored them for five years in 4
>crates (9.5 feet x 4 feet x 4 feet) filled with straw.  While in
>storage large dark gray areas developed.  Mary Lou Florian
>identified the material as alternaria or cladosproium.  The fungal
>structures are not normal hyphae but sclerotic--heavily pigmented
>(melanin) hyphae.

We have had some experience with a similar type of staining, a red
stain, caused by a bacterium called micrococcus. The staining was a
melanin-type substance secreted by the bacteria that becomes
cross-linked to the stone matrix. It feeds on calcitic stones, and
seems to thrive in warm humid environments. It is very common in the
DC area, but I never observed it in New York, where I worked
previously.

We tried a number of things to stop its propagation and remove the
staining. D/2 was moderately successful at stopping it, calcium
hypochlorite was more effective. It frequently occurs in conjunction
with other more common types of biological growth that will be
removed by D/2, so D/2 is likely to significantly improve the
appearance of the affected area for this reason.

But stopping it only succeeded in altering the color of the staining
from red to brown. Nothing we tested was successful in removing the
staining. I did some research into it, but have not had the
opportunity to do any further testing. My research turned up a few
articles, one of which

    J. Delgado Rodrigues and Jesus Valero.
    "A brief note on the elimination of dark stains of biological
    origin", Studies in Conservation (2003) 48 pp 17-22

described success with the use of poultices with Soluene. This
solvent appeared from the MSDS to be quite toxic to all living
things and the environment, and therefore labor intensive in terms
of protection, containment, disposal, etc. It is also expensive. The
few other methods reported to be successful were multiple step
processes that did not seem readily applicable to a site
application. If anyone knows of a material or method that is simple,
practical, and less toxic (not to mention less costly) that is
effective for this purpose, it would be a great contribution.

Robin Gerstad
Conservator
Conservation Solutions, Inc.
503 C Street, NE
Washington, DC 20002
202-544-3257
Fax: 202-544-3229


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                  Conservation DistList Instance 19:25
                Distributed: Thursday, November 10, 2005
                       Message Id: cdl-19-25-007
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