

Strictly speaking, an “illuminated” manuscript contains gold or silver, which reflects the light. A manuscript richly decorated in color only, without actually having gold or silver is, technically, not illuminated. Members of the Cistercian Order were permitted to ornament their manuscripts but not to illuminate them, as gold was thought to be frivolous and inappropriate to an austere way of life. Illumination with gold goes back into antiquity but is especially common in the later Middle Ages. Manuscripts such as Books of Hours are almost always illuminated. If gold leaf is to be applied to a design in a manuscript it is put on before the paint. This is crucial for two reasons. The first is that gold will adhere to any pigment that has already been laid, ruining the design, and secondly the action of burnishing it is vigorous and runs the risk of smudging any painting already around it.

There are several methods of applying gold to manuscript pages and sometimes more than one technique was used in a single miniature in order to achieve different effects. There are three basic types of application appropriate for books. Two methods use gold leaf, and one uses powdered gold. In the first a design is brushed on in some kind of wet glue and the gold leaf is laid on top and is burnished when it is dry. In the second method a sticky gesso is prepared and built up so that the design is really three-dimensional. When the gold has been applied and polished with a burnishing tool it looks extremely thick and the curving edges of the design catch the light from many angles at once. The third method is to apply what is called 'shell' gold, a powdered gold mixed with gum arabic into a kind of gold ink (and commonly dispensed from a sea shell like a mussel or oyster, hence the name) and applied with pen or brush. Unlike leaf gold, it was added after the color.

Gold leaf is not especially easy to use either. It is a property of gold that, unlike many other metals, it can be hammered thinner and thinner without ever crumbling away. A piece of gold leaf is infinitely thinner than the thinnest paper. It is virtually without thickness and has almost no weight. If dropped it hardly seems to flutter downwards. If it settles on a hard surface ruffled or folded it can be straightened out with a puff of breath, straightening itself instantly like a shimmering shaken blanket.

The production of gesso for raised gilding is not difficult, but takes time, as it requires slaked plaster of Paris, which takes about a month to prepare. It can also be dangerous, as white lead is used to make the gesso hard enough to withstand vigorous burnishing without crumbling. Beginning with slaked plaster of Paris, a little white lead is ground in (less than a third of the amount of the plaster). The mixture is very white and crumbly. Then a little Armenian bole is added to supply color. When the gesso is eventually applied to the white page the inclusion of a colored pigment will make the mixture easier to see; and if the gold should ever wear off in places, a pink-brown color underneath gives a more pleasing and warmer glow than stark white. At this point, a dash or two of sugar or some honey is added. These are hygroscopic (has the property of attracting moisture) and it is important that the concoction should remain damp as long as possible. The substance can be dried into little pink pellets and stored like this. When it is needed it is ground up and mixed with a little clear water and glair, crunching the mixture over and over with a palette knife until it is really smooth and runny, without bubbles. Glair is made from the sticky liquid that forms overnight at the bottom of a bowl of whipped egg whites. The froth is discarded, leaving the liquid glair. A small amount of ear wax was often added to the gesso to help eliminate air bubbles which could burst after the gesso’s application to the parchment, creating unsightly craters in an otherwise smooth gold surface.

Gesso is applied with a quill pen, or a brush. Speed is important, as is a lightness of touch so as not to scratch the parchment with the nib. The liquid is puddled into the center of the part to be gilded and then quite quickly drawn out carefully into the corners and allowed to dry. Sometimes a blade is scraped gently over the dried gesso to flatten it out and reduce any unevenness in the surface, as when the gold is applied every flaw will appear to be magnified under the shiny gold surface.