Exterior terra cotta ornaments

Jane Tisdale <jtisdale [at] mailserv__mta__ca> writes

>... fill losses and to remove dark deposits by "gentle washing"...

We just cleaned our building's limestone facade using the JOS
system, and we are very pleased with the results.  The system is a
low pressure wash using a dolomite-water mixture (glass beads can
also be used for more aggressive "scrubbing").  It managed to remove
black carbon deposits without damaging the stone surface.  Because
limestone is soft, we didn't want to use a high-pressure water wash
for fear of surface damage; and the gentlest chemical treatment we
looked into was still pretty nasty.  Also because of the porosity of
limestone, it would have been impossible to rinse out 100% of the
chemicals--so chemical cleaning was also out.  That left a
particulate system, but most of the standard ones in use we felt
were also too aggressive.  When we came across the JOS system
(originally developed in Germany), it looked like it was exactly
what we wanted--and we weren't disappointed.

Joice Himawan
Conservator
Massachusetts Historical Society

                                  ***
                  Conservation DistList Instance 11:76
                 Distributed: Wednesday, March 11, 1998
                       Message Id: cdl-11-76-007
                                  ***