Sandstone rocks at Twyfelfontein are covered by the so-called desert varnish, a hard patina that appears brown or dark grey. Engravings were effected by chiseling through this patina, exposing the lighter rock underneath. The indentations were created over the course of thousands of years. The oldest engravings might be as old as 10,000 years, and the creation of new works probably ended by the arrival of pastoral tribes around 1000 AD.