Glossary · Materials
Tempera
Paint using egg yolk (or occasionally whole egg, egg white, or casein) as the binding medium — fast-drying, luminously precise, and the dominant painting medium in Italian panel painting before oil paint displaced it in the late 15th century.
Definition
Egg tempera is made by mixing dry pigment powder with egg yolk (or whole egg) and a small amount of water. The egg proteins bind the pigment and, when dry, create an extremely hard, stable film. Characteristics:
- Fast drying: Each stroke dries within seconds — blending is almost impossible
- Precise marks: Tiny, controlled brushstrokes are required; hatching builds gradients
- Brilliant color: Pigments retain their pure hue without the yellowing of early oil mediums
- Durable: Centuries-old tempera panels survive in excellent condition when well protected
The Transition to Oil
Northern European painters — particularly Jan van Eyck — refined oil paint as a primary painting medium by the mid-15th century. By the 1470s–1490s, Italian painters were increasingly adopting oil. Leonardo was among the early and most innovative Italian adopters of oil technique, exploiting its slow drying time to develop his sfumato glazing method — something impossible in fast-drying tempera.
The Last Supper Exception
For the Last Supper (1495–98), Leonardo appears to have used a tempera-based technique (possibly mixed with oil) on a specially prepared dry wall surface — deliberately avoiding true fresco. The combination of tempera on a wall (rather than on a panel over gesso) proved catastrophically unstable. The paint could not bond to the stone surface as true fresco bonds to plaster, and deterioration began almost immediately.