The science of ancient paint
The Fayum portraits owe their startling preservation to two factors: the dry Egyptian climate and the chemistry of their materials. Artists in Roman Egypt created these panels using either tempera (pigment mixed with an animal-glue binder) or, more commonly, encaustic painting. The encaustic method required mixing pigments with hot beeswax, sometimes with oils or resins added to alter the texture and drying time. This wax medium was applied in layers while warm, allowing artists to blend colors and create a depth and translucency that looks like skin tones.
The wooden panels themselves were a valuable commodity. Scientific analysis shows that many portraits were painted on imported wood, with European lime tree (Tilia europaea) being a frequent choice. Other identified woods include oak, sycamore, cedar, and fig. The pigments came from several sources. Iron oxides provided red and yellow ochres, while carbon was used for black. Artists also used a synthetic pigment called Egyptian blue, a type of calcium copper silicate first created thousands of years earlier. Non-invasive imaging techniques, such as visible induced luminescence (VIL), can make this blue pigment glow white in infrared images, revealing its use even when mixed with other colors.