Can dispersed and migrated arsenic from degraded pigments in paintings be a marker for water-linked transport processes?
Chemical degradation of emerald green (Cu(C2H3O2)2-3Cu(AsO2)2) and photo-degradation of orpiment (As2S3) and realgar (As4S4) in oil paintings have arsenic trioxide (As2O3) as a common degradation end product. In such paintings, arsenic is no longer confined to the pigment particles, but is detected with elemental X-ray analysis throughout the whole paint system, e.g., at layer interfaces, in varnishes, around iron- and aluminium-containing particles and in the wood structure of a panel painting. Several case studies are presented. The migrated arsenic is thought to be transported within the paint system as arsenic trioxide in aqueous form by the same mechanism as its transport in groundwater in the environment. Dispersed arsenic in paintings released from degraded pigments can be a marker for water-linked transport processes.