Application of leaf.When the last coat of the gesso-mordant was dry and hard, its surface was carefully polished with the burnisher and it was then ready to receive the gold leaf; several days' waiting would often be required before the whole body of the mordant had set perfectly hard. White of egg was then lightly brushed over the whole of the raised mordant, and while the albumen was still moist and sticky, the illuminator gently slid on to it the piece of gold leaf, which he had previously cut approximately to the required shape. He then softly dabbed the gold leaf with a pad or bunch of wool, till it had completely adhered to the sticky mordant, working it with special care so as completely to cover the rounded edges. After the albumen was quite dry, and the gold leaf firmly fixed in its place, the artist brushed away with a stiff brush all the superfluous gold leaf; all the leaf, that is, under which there was no mordant-ground to hold it fast.
| Burnishing process. |
Burnishing process.The gold was then ready to be polished. For this purpose various forms of burnisher were used, the best being a hard highly polished rounded pencil of crystal or stone, such as haematite, agate, chalcedony and the like; or in lack of those, the highly enamelled tooth of a dog, cat, rat or other carnivorous animal was nearly as good[[260]]. In fact patience and labour were the chief requisites; one receipt, in Jehan le Begue's manuscript, § 192[[261]], directs the illuminator to burnish and to go on burnishing till the sweat runs down his forehead. But caution, as well as labour, was required; it was very easy to scratch holes in the gold leaf, so that the mordant showed through, unless great care was used in the rubbing. In that case the illuminator had to apply another piece of leaf to cover up the scratches, and do his burnishing over again. To secure the highest polish, illuminators burnished the hard mordant as described above before laying on the gold leaf. In most cases two layers of gold leaf were applied, and sometimes even more, in order to insure a perfect and unbroken surface.
| Application of gold. |
Application of gold.All writers speak of this burnishing as being a very difficult and uncertain process even to a skilled hand, requiring exactly the right temperature and amount of moisture in the air, or else it was liable to go wrong. If the gold was to be applied in minute or intricate patterns the illuminator did not attempt to cut his leaf to fit the mordant-ground, but laid it in little patches so as to cover a portion of the ornament. The superfluous gold between the lines of the pattern was then brushed away, as the leaf only remained where it was held by the mordant. With all possible care and skill, it was hardly possible always to ensure a sharp clean outline to each patch of gold; and so one commonly finds that the illuminator has added a black outline round the edge of each patch of gold, in order to conceal any little raggedness of the edge.
| Receipts for the mordant. |
Receipts for the mordant.As examples of mediaeval receipts for making the mordant I may mention the following:—
"Mix gypsum, white marble, and egg-shells finely powdered and coloured with red ochre or terra verde; to be mixed with white of egg and applied in thin coats, and to be burnished before the application of the gold." When dry, this mixture slowly set into a beautiful, hard and yet not brittle substance, capable of receiving a polish like that of marble, and forming the best possible ground to receive the gold leaf. Much of its excellence depended on the patience of the illuminator in applying it in very thin coats; each of which was allowed to dry completely before the next was laid on. When ready to receive the gold leaf, after the burnishing of the mordant was finished, some purified white of egg was brushed over to make the gold leaf adhere firmly so as not to work loose or tear under the friction of the burnisher.
| Receipts for the mordant. |
Receipts for the mordant.In some cases white lead (ceruse) was added to the gesso, as, for example, in a receipt, given by Cennino Cennini (§ 131 to 139, and 157,) for a mordant made of fine gypsum, ceruse and sugar of Candia, that is ordinary pure white sugar[[262]]. This is to be ground up with white of egg, applied in thin coats and burnished. To colour the mordant Cennino adds bole Armeniac, or terra verde, or verdigris green.