INTERACTION OF HISTORICAL LEAD GLAZES WITH CORROSIVE MEDIA

Abstract

Lead glasses and glazes are often discussed in terms of degradation processes in connection with their wide use in the field of cultural heritage in historical objects of low-fired glazed ceramics and historical glasses. This work is focused on the evaluation of the interaction of lead glazes with a corrosive media simulating environment of waste pits, deposits and possibly inappropriate conservation interventions. The first part of the experiment contains surface characterisation of several archaeological fragments of glazed ceramics. Two model lead silicate fritted glazes for corrosion tests were prepared based on their compositions. A system based on nitric acid solution simulates nitrates in the soil that surround the archaeological finds, and the aqueous solution of acetic acid represents corrosion in complex organic acids and humic acids. The concentration of Pb and Si was determined in corrosive solution by AAS. Precipitates were identified by optical microscopy (OM) and were examined via XRD and SEM-EDS analyses. Vibrational spectroscopy (ATR, Raman) proved that the proportion of Pb representing a function of network former decreases with time. The shift to higher wavelengths indicates a change in Q motifs in the glass structure of the glaze frits or a glass network transition from a Si-O-Pb-O-Si towards a Si-O-Si glass network.

Keywords

• lead glazes
• corrosion mechanism
• microscopy
• spectroscopy
• historical ceramics