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._ 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._ 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._