Preservation and permanence of graffiti art

I am seeking information about the preferred materials used by
graffiti artists.  The query relates to large-scale graffiti "art"
rather than "tagging".  I am particularly anxious to get brand-name
and color-name information so that I can contact manufacturers about
the weathering performance of relevant products

I am also interested in barrier films to intervene between the
original graffiti and any further graffiti which may be added on
top.  These seem to divide into "permanent" epoxy or polyurethane
coatings and sacrificial alcohol-copolymers but I would be
interested to hear from anyone who has tried using any of these
systems.

Any information, personal experience, or literature references would
be appreciated.

JP Brown
Environmental Conservator

                                  ***
                   Conservation DistList Instance 9:7
                   Distributed: Monday, July 10, 1995
                        Message Id: cdl-9-7-010
                                  ***