Egg yolk paint outlasts oil because its colours never yellow
For most of European painting before 1500, the binder was egg yolk. Tempera dries fast, lays down in fine hatched strokes and, unlike oil, never darkens or yellows with age. Its oldest known traces sit in Sardinian tombs from 3400-2700 BCE, and it even seeded the invention of Liquid Paper.
Tempera is pigment ground into a water-soluble binder. Egg yolk gives egg tempera, milk protein gives casein, and synthetic PVA gives yet another version; the school poster paint sold under the same name uses starch or gum and behaves more like gouache. The word comes via Italian from a Late Latin verb meaning to mix thoroughly. Evidence of the egg medium turns up in the Domus de Janas chamber tombs of Sardinia and, around 1200 BCE, in the murals of the Palace of Nestor at Pylos. Claims about Egyptian sarcophagi are shakier: recent analysis shows ancient painters there usually preferred animal glue.
Byzantine icons, medieval manuscripts and Early Renaissance panels were almost all tempera. Most panels attributed to Michelangelo use it, with his Doni Tondo mixing in oil. Oil paint, perhaps originating in Afghanistan between the 5th and 9th centuries, displaced it in the Netherlands during the 15th century and in Italy around 1500. Orthodox icon painters in Greece and Russia never stopped using it, sometimes adding myrrh to mask the eggy smell.
Making it is fiddly. Painters separate the yolk, pierce its membrane to drain the contents, and usually thin it with about three parts water, though some recipes use white wine; a dash of vinegar keeps it a week but can discolour ultramarine, so fresh daily batches are better. It needs a rigid, absorbent ground such as gesso on wood panel, three to six months to cure, and no glass over the finished work, which could trap moisture and breed mould. It cannot be built up thickly, so colours are less saturated than oil and look rather like fresco until varnished. Tubed versions from Sennelier contain oil, making them tempera grassa, which Marc Chagall used heavily.
Revivals kept returning. William Blake and the Pre-Raphaelites took it up; an 1821 publication of Cennino Cennini's handbook and the founding of the Society of Painters in Tempera in 1901 spurred a wider return. In America Andrew Wyeth and Jacob Lawrence worked in it, and Bengal school artists such as Nandalal Bose made it central to modern Indian painting.
Source: Tempera
