Efficacy of acid treatments used in archaeological ceramics for the removal of calcareous deposits

Abstract

Calcareous deposits are one of the most common alterations that archaeological ceramics can exhibit, and they can damage their artistic and historical values. For this reason, it becomes necessary to remove these deposits. However, there is no agreement in the conservation field about the conditions of the cleaning treatments. Moreover, little has been studied about the consequences that archaeological ceramics might suffer. The main purpose of this research is to study the efficacy and safety of several cleaning treatments that are or can be used in archaeological ceramics. To this aim, it was necessary, in first place, elaborating ceramic specimens, simulating archaeological ones, and artificially growing calcareous deposits on their surface. Afterwards, effective and little damaging cleaning treatments based on the immersion of the elaborated ceramics on acid products were developed. Acetic and nitric acid solutions were prepared at the minimum concentration and applied during the minimum time to be effective. Ceramic specimens were elaborated with a commercial red clay simulating archaeological ceramics to avoid trials on real cultural objects. The mineralogical composition of the ceramics was studied by X-ray powder diffraction to establish if changes occurred after the carbonation process and after the cleaning treatments, and thermogravimetric analysis allowed to quantify the calcium carbonate content in every step of the process and to determine the efficacy and safety of such cleaning treatments. According to the results obtained so far, the acid treatments (acetic and nitric acid) were both effective in the removal of the deposits and did not modify the initial mineralogical composition of the ceramic specimens. Besides, no significant differences among them were detected regarding their efficacy.