The mode of formation of thecotrichite, a widespread calcium acetate chloride nitrate efflorescence

The widespread occurrence of thecotrichite, Ca3(CH3COO) 3Cl(NO3)2·7H2O, in the museum environment is explained theoretically by construction and examination of its phase diagram. Thecotrichite formation was simulated in the laboratory to identify the key factors involved in its production. This efflorescence occurs on porous limestone or calcareous artefacts such as pottery, stored in wooden cabinets that generate acetic acid vapour. Salt production depends on the moisture content of the object and the concentration of acetic acid in its surroundings. Furthermore, for thecotrichite to form the artefact must contain soluble chloride and nitrate salts.