The use of varnish as a relative and absolute dating tool for engravings is reviewed. Absolute dating of varnishes has been undertaken in the USA, where cation ratios in varnish on rock surfaces of known age, and in present-day soils have been related to ratios within rock engravings. Investigations in western New South Wales have been directed towards determining the chemical and morphological characteristics of varnish, its age, and local distribution. A minimum age for varnish development has been suggested by radiocarbon dating of carbonate partly coating varnish. Future work on varnishes having possibly different ages will be carried out using PIXE, SEM, and the electron microprobe.