Salt degradation of historic Portuguese azulejos

Abstract

The glaze layer degradation of a set of Portuguese tiles from the XVII to the XVIII centuries has been researched. Within this study ageing tests were performed aimed at investigating a method for the simulation of azulejos physical decay. The ageing due to the presence of NaCl salt and various conditions of drying temperature and water saturation have been imposed to the set of tiles that presented different characteristics and defects on their glaze layer. These defects were caused by previous degradation or production faults. The results showed that sample characteristics such as the porosity, vapor permeability and drying rate were decay drivers, but the existence of some particular glaze defects proved to be the most critical one.