Removing permanent marker from porous stone

I am cleaning a stone sculpture (volcanic tuff) with tags written on
with different permanent markers--solvents only worked with "paint
markers", for the black and red writings I also tried hydrogen
peroxide, without effort. Is it possible to bleach it, e.g. with
sodium hypochlorite, or is the ink pigmented?

Olaf Pung
Conservation of stone objects
Thuer, Germany


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                  Conservation DistList Instance 25:3
                   Distributed: Sunday, June 19, 2011
                        Message Id: cdl-25-3-019
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