Verdigris refers to the copper salts of acetic acid, which have different chemical compositions and could range from a green to a bluish-green colour^: 132. Verdigris has been used for artistic purposes from antiquity until the late 20th century, such as for easel painting, polychromatic sculptures, and illumination of maps. Verdigris was a common ingredient in colouring agents, and pharmaceutical preparations^: 414. The leading production site was in Montpellier, where it became a women dominated industry^: 172. Until the 19th century, verdigris was the most vibrant green pigment available and was frequently used in paintings. However, due to the colour being subjected to colour change, the popularity of the pigment dissipated in as more alternatives for other green pigments became readily available^: 171. Factors that contribute to the colour variation on verdigris relies on the hydration level and basicity, which changes as the pigment interacts with other pigments or during the process of ageing^: 637.