Soluble Salts Extraction with Different Thickeners: Monitoring of the Effects on Plaster

Soluble salts content and their crystallization play an important role in the deterioration of porous substrates; the common approach to solve this conservative problem is focused on the identification of a proper thickener and application protocol able to reach a good level of desalination. Here we report the results of a systematic study on a late Renaissance plaster aimed at reducing the content of gypsum and sodium nitrates comparing five different type of thickeners. The extractive process has been monitored by Evanescent Field Dielectrometry (EFD) by means of the evaluation of salinity index (SI) and humidity content (HC), whereas the quantification of the salinity level, before and after desalination, has been performed with ionic chromatography (IC). Data coming from the field, have been integrated with laboratory measurements aimed at evaluating the water release trend, according to the micro-structural features and the pore size distribution of both the thickeners and the substrate. This step has the purpose to identify an effective correlation among the characteristics of the desalination systems and the porosity in order to estimate a proper trend of effectiveness, suitable for the procedure of conservators.