Lichen: the challenge for rock art conservation
Debra Elaine Dandridge
Chair: Smith
December 2006
This study investigates the effects that lichens have on rock surfaces in which ancient
rock art (petroglyphs and pictographs) may be found. The study area includes four sites
in the United States: one quartzite site in southwest Minnesota, two sandstone sites in
Wyoming, and one volcanic site in Central New Mexico. One additional granitic site
studied is located northeast Queensland, Australia. The questions driving the pursuit of
this dissertation research are: 1. How does the chemistry of the rock change with
weathering and how deep is the profile? 2. Do lichens cause differential chemical
changes? 3. How does the chemistry of the unaltered rock influence these changes? 4. Do
lichens strip the patina or “desert varnish― from the rock surfaces? The
results of this research confirm from elemental chemical analyses that geochemical
changes do take place in the presence of lichens. The combined mechanical and chemical
processes contribute to the degradation and greater erodability of all the rock surfaces
studied. Chemically, we have demonstrated that cements that hold grains of rocks
together can be dissoluble by lichen byproducts in the presence of an aqueous
environment whether the rocks are sandstone or granite. This information regarding the
mechanical and geochemical processes at work in natural environments has significant
practical benefit for the management, conservation, and preservation of rock art sites
everywhere.