Glossary · Materials
Gesso
A smooth, brilliant white ground layer applied to a wooden panel before painting — created from chalk or gypsum mixed with animal glue (size). Provides the luminous base from which all subsequent paint layers derive their brightness.
Definition
Gesso (Italian: chalk or plaster) is a preparatory ground made from calcium carbonate (chalk) or calcium sulphate (gypsum) mixed with animal hide glue. Applied in multiple coats to a prepared wood panel — which had first been covered with a linen canvas to prevent cracking — gesso creates a smooth, hard, brilliant white surface for painting.
Italian Renaissance panels typically received many coats of gesso applied in alternating layers of gesso grosso (coarse) and gesso sottile (fine, polished). The final surface was sometimes scraped with a knife until nearly as smooth as ivory.
Why It Matters
The brilliance of Renaissance tempera and early oil painting depends on the reflectivity of the white gesso ground. When an artist paints a translucent glaze over white gesso, light passes through the paint layer, reflects from the white ground, and passes back through the paint — creating the luminous "glow from within" effect that distinguishes Renaissance panel painting from later works on darker grounds.
Leonardo applied a white lead ground to the Last Supper wall in lieu of gesso to achieve a similar brightness effect on the stone surface.