Formation of acetate salts in museum environments
Acetate salts are frequently observed in efflorescences on calcareous objects in museum cabinets. Their formation is the result of the attack of acetic acid emitted by wood and other materials that are used for the construction of display cases. The low air exchange rates in typical display cases and storage cabinets provide favorable conditions for the enrichment of acetic acid and other volatile pollutants liberated by these materials. A number of different acetate salts were identified in efflorescences on museum objects including calcium acetate, the double salts Ca(CH3COO)Cl·5H2O and Ca2(CH3COO)3(NO3)·2H2O and the triple salt thecotrichite, Ca3(CH3COO)3Cl(NO3)2·7H2O. Objects are severly damaged by the growth of these compounds (see photos below). In close collaboration with the conservator Lieve Halsberghe we have carried out an extensive analytical study to characterize the efflorescences on Dutch tiles of glazed ceramics [1]. To understand the formation of the various double and triple salts we have established the phase diagram of the quaternary thecotrichite system [1,2]. For the modeling of the phase diagram of this system we use a Pitzer type electrolyte solution model for acetate and formate salts [3-5]. Currently, we are extending this approach to more complex mixtures of calcium acetate with inorganic salts.
photos by Lieve Halsberghe (Ceramics Conservator, Brussels)
Publications
- Linnow K., Halsberghe L., Steiger M., J. Cult. Heritage 2007, 8, 44–52.
- Gibson L.T., Cooksey B.G., Littlejohn D., Linnow K., Steiger M., Tennent N.H., Stud. Conserv. 2005, 50 284–294.
- Steiger M., Beyer R., Dorn J., A thermodynamic model of the Na-Ca-Cl-CH3COO--H2O system. In: Price C.A. (ed.) ECOS: Environmental Control of Salts. Protection and Conservation of European Cultural Heritage Research Report, 2000, 45-52.
- Beyer R., Steiger M., J. Chem. Thermodyn. 2002, 34, 1057–1071.
- Dorn J., Steiger, M., J. Chem. Eng. Data 2007, 52, 1784–1790.