fire damaged stone

["Heather Lawson" <raspberrybaystone@zzzzzzzzzzzzzzz>]

I often do conservation and restoration work on heritage gravemarkers, primarily sandstone, limestone and slate.
Occasionally these include stones that have been burnt (seems it was a form of yearly lawn maintenance in the
not so distant past) when it is necessary to clean these stones for repair we have had great success using a
soft brush and water.  If the stone already has a patina, or is of a harder nature as with granite, little of the soot
will have migrated into the stone.  I find we often get too aggressive in our approaches too quickly.  All methods
of cleaning stone have their draw backs, on the softer stones no matter what the method used, grains of the
stone are removed, so I always feel it is best to start with the least invasive method first, analysis the results,
then if necessary move up the ladder.
If the stone I am working on is stable with little wear I will use a brass brush and lots of water.  Starting at the bottom
and working upwards. If the stone is still not to satisfaction I would use a non-ionic detergent like Photo-Flo (you
can get this from a photo supply store) at 1oz. to 5 gal. of water or similar products from conservation supply stores.
The stone should come clean, it may not be as perfect as before but everything carries the scars of  life, it helps to
tell its story.
Heather