Alteration processes of pigments exposed to acetic and formic acid vapors

This contribution investigates the chemical modifications experienced by different historic inorganic pigments when exposed to acetic and formic acid vapors naturally produced by wood. The production of acetic and formic acid vapors by wood is well known phenomenon; their interactions with different materials as metals, limestone or glass were already investigated, but only few researches concern interactions with pigments. Pigments modification processes represent one of the most important causes of artworks deterioration since they are directly involved in the pictorial films and their colors. Polychromatic artworks, such as paintings or manuscripts, are generally held indoor where they could be directly exposed to the acid vapors produced by wood floors or cases. In order to study the interactions between pigments and acid vapors, Azurite, Red Lead, Tin-Lead Yellow, and White Lead pigments were selected on the basis of their chemical composition and historical wide use. Powders of these materials were exposed in a simulated acetic and formic acid environments and their alteration processes were investigated by XRD and SEM analyses. The assessment of chromatic variations was performed through a colorimeter.