REMOVING CALCIUM CARBONATE DEPOSITS FROM ARCHAEOLOGICAL CERAMICS. TRADITIONAL METHODS UNDER REVIEW

Abstract

Although insoluble salts are one of the most common alteration forms that archaeological ceramics can pre

sent, the methods for their removal have not really changed within the past forty years. Furthermore, not

many studies on the topic have been recently published. In this paper, a methodology to study the suitability

of different traditional treatments for the removal of these salts, has been established. For this aim, ceramic

mock-ups made out of a marketed red clay were fired up to 700ºC in an electric kiln. Their composition and

physical properties were studied. Several tests were conducted in laboratory for the growth of calcium car

bonate deposits similar to the ones that can appear naturally on archaeological ceramics. The method that pro

vided the more alike deposits, was followed and applied onto the ceramic mock-ups. Different cleaning treat

ments based on three chemical products and three application methods were put into practice for the removal

of such deposits. The products included two acids and a chelating agent and the application methods were

direct and indirect, by immersion and using pulps and gels. The specimens’ characteristics were studied again

to determine their changes due to the cleaning treatments. The analytical techniques of XRD and SEM, for

mineralogical and elemental composition, microroughness, colour measurements, stereoscopic microscopy

were used, and results showed efficacy differences linked to the product and application method. In general,

the products applied by immersion and cellulose pulp poultice were more effective than gel treatments, which

were less effective with any of the three products tested.