Pigment binder

I have been volunteering in the National Parks, gently sandblasting
spray paint graffiti from granite then touching up the damaged
pre-existing natural mineral stains by airbrushing with mineral
pigments and water, and was looking for suggestions for a non-toxic
airbrushable binder for mineral pigments that won't attract microbes
or other flora.  I'm assuming the gum arabic used for watercolor
painting is not the answer, as that is organic and would grow flora?
suggestions?

Zack Peabody
NPS Volunteer
San Diego


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                  Conservation DistList Instance 29:5
                   Distributed: Friday, June 19, 2015
                        Message Id: cdl-29-5-009
                                  ***