Desert varnish or rock varnish is an orange-yellow to black coating found on exposed rock surfaces in arid environments. Desert varnish is approximately one micrometer thick and exhibits nanometer-scale layering. Rock rust and desert patina are other terms which are also used for the condition, but less often.
Desert varnish on gibber, Central Australia
Desert varnish on Bishop Tuff.
Petroglyphs carved in desert varnish at the Valley of Fire near Las Vegas, Nevada. Area shown is about one metre across.
Desert varnish at Capitol Reef National Park
Varnish is a clear transparent hard protective coating or film. It is not to be confused with wood stain. It usually has a yellowish shade due to the manufacturing process and materials used, but it may also be pigmented as desired. It is sold commercially in various shades.
Varnish on wood stairs
Varnished oak floor
A table green wood-stained and varnished with three layers of polyurethane varnish