The varied visibilities of petroglyphs I find of great interest. As light changes, my apprehension of the image and stone changes. My feeling for the image and its relationship to the stone's color and texture, its cracks and curves, and to the surrrounding environment shifts. Older glyphs would have appeared quite dfferent in brightness and contrast when first pecked or carved. Differential weathering, desert varnish (patina), and lichens can greatly affect how related glyphs are perceived. This is particularly acute with strong sun shadowing.
Photographs by Douglas Beauchamp, 2012-2014, Southeastern Oregon
For related blog post, Dec 21 2014: Presence of The Dark