‘Ilumination’ refers to the painted decoration of a medieval manuscript (a hand-written and painted book), usually on parchment (prepared animal skin such as sheep, goat, pig or calf). The word is derived from the Latin illuminare ("to light up") because of the glow created by the radiant colours along with gold and silver leaf, which is often burnished to a high shine.

Traditional binders for making paint in illuminated manuscripts:

Dry powder pigment, the illuminator’s source of colour, are mixed with a binding agent or medium. The binder allows the pigment to adhere to the parchment surface and works to preserve the colour over time.

Egg glair was the main binding agent used in manuscript illumination up until the late 14th century. Untreated egg white, being slimy and irregular in consistency, is unsuitable to make smooth paint. When ‘clarified’ to make egg glair, the medium is runny, smooth, and sticky. To make egg glair by the medieval method, beat an egg white to a stiff foam, leave it overnight, skim away the froth, then extract the clear liquid. Medieval illuminators preserved their glair by encasing the solution between two broken egg shells, which allowed a degree of air to circulate and thus prevented rancidity.

Medieval egg glair recipe

When a mix of pigment and glair alone is painted onto the malleable parchment, cracks sometimes developed. A little honey was often added to the mixture, allowing greater flexibility and paint viscosity. Earwax, too, was also recommended to inhibited the formation of froth in the medium!