Colorimetric evaluation of the presence of efflorescence in red clay ceramics with calcium and sulfate ions

Efflorescence is a pathology quite frequently observed in ceramics. However, it has not yet been developed a methodology capable of quantifying this process's advance or its onset manifestation with precision. In this context, this paper proposed a method that uses colorimetry measurements to identify the presence and also quantify the efflorescence phenomenon. For the proposed methodology validation, red clay samples with added amounts of calcium sulfate (5; 10 and 15 % wt.) as an efflorescence agent were prepared by uniaxial pressing, following heat treatment at 900, 1000, or 1100 °C. To produce the efflorescence phenomenon, samples were then immersed in ultrapure water, only half of their height, for 21 days and then dried in the open air. After the heat treatment, the samples were also characterized by apparent porosity, water absorption, the presence of soluble salts in the fired clay, and water penetration capacity. It was possible not only to identify with precision the onset of the superficial efflorescence phenomenon but also to quantify it in a reliable way using the colorimetry method proposed since even small amounts of calcium sulfate crystals are capable of changing the light reflectance index of the original surface, which is easily detected by a colorimeter