The traditional form of painting in which the artist ground pigment and bonded it together with pure egg yolk. Egg Tempera paintings are long lasting and specimens from 1st centuries AD a still with us today. It was a primary method of painting until after 1500, by when it was superseded by the invention of oil painting.
As a painting medium it has great many advantages such as being able to paint extremely fine lines. But there are two important drawbacks. One is that the paint dries quickly, the other is that gradations between two colours only really is possible by either cross-hatching fine lines or by making blends of the two colours and add zones for each intermediary mix.
As an example, Botticelli’s Birth of Venus is painted using egg tempera.