Dorn (1983) has proposed that changes in rock varnish chemistry can be used to date varnished artifacts. Specifically, he suggests that the varnish cation ratio, (K + Ca)/Ti, decreases as the age of the varnished surface increases. Although the method is generating significant archaeological interest, many of its underlying assumptions remain undemonstrated. This paper examines one premise of the method, that the varnishing process is regular. Data obtained from varnish distributional studies challenge this assumption and, when compared with the chemical data obtained from the same archaeological site, suggest that the cation-ratio dating technique may not be able to provide accurate dates for most varnished artifacts.