Sandstone

I recently examined an Egyptian sandstone relief which was purchased
at auction by a private individual. When she bought it three months
ago it was clean. It now (3 months later) displays a 'rash' of spot
stains which has progressed during this time over the top two
thirds. It appears to be mold staining--the spots are black and
brown in colour. I initially thought to use a biocide but have asked
the owner to ask for any conservation records the auction house may
have and details of storage conditions prior to sale. The apartment
it now stands in has an ambient temperature, is  airy and free from
damp.

There is little surface crust to these spots and they travel through
the piece to the back (about 2 ins). If they have not occurred
naturally could they be the result of a conservation treatment prior
to the sale? Does anyone have a similar experience and what methods
would you propose to halt its progress?

Jane Foley


                                  ***
                  Conservation DistList Instance 16:2
                  Distributed: Thursday, June 20, 2002
                        Message Id: cdl-16-2-012
                                  ***