Mold on stone

Robin Gerstad <robingerstad [at] conservationsolution__com> writes

>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. ...
>...
>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. ...
>...
>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. ...

Since Soluene was judged effective for a certain dark staining, I
wonder if the mycelium are protected by a naturally produced waxy
substance that prevents normal agents from working.  If a solvent
normally used to dissolve waxes like VM&P naphtha or
trichloroethylene (also bad environmentally!) were used in a
poultice, followed by the regular stain removing procedures, like D2
and/or hydrogen peroxide, I wonder if the results would be better.
Just a thought to add to the possibilities.  I was under the
impression, though, that hypochlorites were not generally advisable
on stone.

Linda Roundhill
Art and Antiquities Conservation, L.L.C.
Woodinville, WA
USA


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                  Conservation DistList Instance 19:26
                Distributed: Saturday, November 19, 2005
                       Message Id: cdl-19-26-006
                                  ***