(Slide 4) After dating pictographs in five regions of Canada, the US and Mexico, I chose the West Coast and adjacent Plateau to find Salish art of the same period and culture. I felt this would improve their interpretation and stylistic dating which are subjective. We now have pictograph dates at Lil’Wat near Whistler in British Columbia and the Okanogan in Washington State. Research shows most world art is engraved, so I adapted my method to petroglyphs. As Salish pictographs and petroglyphs are weathering quickly, we enhanced them to show hidden motifs and palimpsests. They suggest different stages of art production occurred, complementing our buried rock art in many levels.
(Slide 5) I knew that pigment rendering as seen here with a camera would not work for dating petroglyphs, but thought soil sifting would separate rock art debris. Attendees at the 2010 IFRAO Conference in France understood my pictograph dating, but said petroglyphs could not be dated that way. I told them my petroglyph dating was not based on pigment but on buried hammerstones or their chips, line grinders and the rock flour they make, as well as fallen chunks of parent rock. We used rough air vent screens to capture larger rock art debris and finer screens like flour sifters and tea strainers for rock flour and tiny hammerstone particles. Filter-clogging clay and silt in some soils was removed by suspending in water, decanting and filtering.