Visual examination of works painted with water-soluble encaustic

Because of the soap content, brushstrokes of beeswax-and-soap encaustic painting often show formations of small craters in their surface caused by air bubbles trapped in the paint. These craters are a visual feature of works done with water-soluble encaustic and can be considered as fingerprints that allow a visual identification of this technique. At left, crater formations observed in contemporary paintings done with water-soluble encaustic.

At left, similar crater formations can also be found  in Roman-Egyptian portraits of Fayum, in Roman wall paintings, and in the cold-applied brushstrokes on Greek ceramics.

Top, crater formations observed in brushstrokes in Roman wall paintings.

Bottom, craters in brushtrokes on Greek vase. These brushstrokes, usually white, yellow or purple in colour, have a thicker and less shiny appearance and a poreer durability than the black glaze brushstrokes also present in these vases. Chemical analysis of these thick brushtrokes showed presence of beeswax and soap, indicating they could have been painted with water soluble encaustic.
Source: José Cuní and Jorge Cuní. Naturaleza de los colores fugitivos en la cerámica griega. Archivo Español de Arqueología, 65, 1992, 302-303.