This month an exhibition of paintings by Piero di Cosimo – Renaissance Italy's answer to Hieronymus Bosch – travels from the National Gallery of Art in Washington to the Uffizi in Florence, bringing home until 27 September a collection of lilac skies, lifeless trees and unfathomable creatures.
As much as I admire the oil paintings, my eyes will be fixed on the paintings Piero rendered in egg tempera, a mixture of colour pigment, egg yolk and clove oil or vinegar. It's not their subject matter, nor even their bold colour that confounds me, but the mind-aching enigma of what Piero did with all his leftover egg whites.
Where, I ask myself, did all the egg whites go? Where did any of the great artists' egg whites go? Such luminaries as Leonardo da Vinci, Raphael and Botticelli were among those who mixed yolks to make tempera even after oil painting had become the vogue, appreciating how opaque and luminous it made their subjects' flesh, and how quickly it dried.
Piero, who for a time ate nothing but eggs, setting 50 or more to boil at once alongside the glue he heated to seal his paintings, used tempera to paint the nude mythological figures of his Tritons and Nereids. If he followed the advice of a handbook available at the time, he would have used the yolks of town hen eggs for the females' pale and youthful skin, and those of country eggs (considered ruddier) for the swarthier complexions.
But the question remains: what did he and the others do with the whites? Leonardo, exemplifying one possible use, boiled eyeballs in egg whites to make them easier to dissect for his anatomical drawings; many painters added whites to the gloss for their paintings.
Perhaps another answer lies in Europe's first cookbook, which contained recipes from the court where Leonardo was based. The author, Bartolomeo Sacchi, known as Platina, filled it with dishes he had learned from a Maestro Martino, onetime court chef for the Sforza family in Milan. On Honest Pleasure and Good Health, which he began writing around 1464, was printed in 1475, seven years before Leonardo arrived as painter at that very court. Piero di Cosimo was then 13 years old.
Lo and behold, the book's recipes are peculiarly rich in egg whites. While we would normally use yolk or whole egg to make pasta, Maestro Martino advised making vermicelli and Sicilian macaroni from flour, rose water and egg whites.
His herbe torte is to be made with 15 or 16 egg whites, no yolks. White torte combines 12 or 15 egg whites with cheese, lard, butter, milk, sugar, and ginger. Fritters, a variation, perhaps, on the modern tempura batter (no relation to egg tempera), required egg whites and flour.
Even where the standard recipe called for egg yolks, there were alternative "white" versions, such as white broth and white dumplings.
While some of Maestro Martino's recipes must have been circulating since medieval times, Platina ensured that they were disseminated across Europe. From Venice the book travelled to Louvain, Bologna, Strasbourg, Cologne, Paris, Lyon and Basel.
Based at the court where Maestro Martino had worked his magic, Leonardo must have been among the first to taste his recipes – especially because he was vegetarian. Indeed, he remarked upon the variation of flavour combinations in the finished cookbook.
But this was not the egg's only contribution to the Renaissance. To win the commission to design the roof of the Florentine Duomo, Santa Maria del Fiore, Filippo Brunelleschi challenged his rivals to make an egg stand unaided on a piece of marble.
No one could do it, until Brunelleschi set it down firmly enough that the bottom of the shell cracked – without piercing the egg sack inside – to produce a flat base. He won the commission and, wasting no time on hefty arches and supports, built a slightly flattened dome within a dome, just like the sack-lined egg. The trick became so famous that it was also attributed to Christopher Columbus as he showed that discoveries, such as that the world is round, are only obvious after the fact.
It is truly sobering to think that, through all the achievements of the time, the egg, in its various component parts, might just have provided the sustenance by which the Renaissance was nourished.
Harry Eyres is away