Analysis of Salts and Clays for Conservation of Porous Cultural Heritage

Abstract

Soluble salts and clays are major intrinsic causes of degradation of porous cultural heritage materials. Identifying their presence and concentrations can allow environmental control to prevent decay before it is observed. Such control is often energy- and carbon-intensive and better targeted towards those objects that require it rather than a general approach. The use of poultices has been investigated to determine salt species and concentrations in stone to replace drilling samples. A non-invasive method using two types of moisture meter has been developed to map the conductivity of salt solutions in stone. Fourier transform and near-infrared spectroscopies have been investigated to non-invasively quantify the amount of muscovite clay in limestones without the need to take drilled samples. Salts can react with extrinsic acetic acid from display and storage environments, causing extensive damaging surface efflorescences. A rapid analytical procedure based on external reflectance Fourier transform infra-red (FTIR) microscopy has been developed. This allows analysis of multiple salts on a cuneiform tablet surface. Analyses of soluble salts inside the tablets has indicated the sulphate-to-chloride ratio is a good predictor of whether mixed acetate efflorescences will occur on exposure.

Keywords

• FTIR
• NIR
• poulticing
• soluble salts
• mixed acetate salts
• clay