Removing ink from marble

Suzanne Hargrove <objcons [at] slam__org> writes

>An outdoor Knoxville Marble sculpture was recently vandalized with a
>black felt tip pen.

I have found that time-tested traditional methods still sometimes
work the best.  Certain clays make the most amazing poultices for
light colored stone.

I don't know what the final word on Attapulgite is.  Though it has
received bad press because of its needle-like microstructure
structure (resembling asbestos), a mineralogy expert I spoke to
insists that it is no more dangerous than working with any
silicate-type product and needs to be handled accordingly.

Attapulgus clay (also known as Palygorskite and sepiolite in
England) is a highly absorptive natural clay with many chemical bond
sites available while the clay is drying.  A thick slurry in tap
water applied liberally, at least 3/4 inch thick and allowed to
partially dry until it lifts off in pieces will draw most metallic
and organic stains into the clay.  Furthermore, thanks to the
hydro-chemistry of the clay crystals and unique tubular channels,
the staining substances are locked in so they do not spread, do not
get driven into pores, nor re-deposit (unlike some poultice
techniques). Adding a little alcohol to the water may also encourage
dissolution of the ink, but too much may interfere with the
hydro-chemistry of the clay.

Kaolin and Montmorillonite are related clay minerals, but are not
quite as effective.  I hope they give the OK on Attapulgite soon,
because it is truly superior in many ways to other treatments.  Has
anyone heard any updates?  I will doing some trials with zeolite
clay poultices to see if these can perhaps be substituted as these
have similar absorptive qualities.

Linda S. Roundhill
Art and Antiquities Conservation
18121 157th Ave NE
Woodinville WA 98072
425-481-0720


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                  Conservation DistList Instance 15:36
                 Distributed: Tuesday, November 6, 2001
                       Message Id: cdl-15-36-002
                                  ***