The individual titles of this series of paintings list the separate pigments used to make them. The paint layers can be seen at the edges. The artist says that these edges can be read ''almost like a bar code'', making it possible to ''uncover the history of each painting''. They come from a group of fifty such works, which trace the history of painting by classifying and indexing the development of artist''s pigments, from early cave paintings to the present day. The information is taken from a chart produced by the paint manufacturers Winsor & Newton.