Sir Charles Eastlake, who has profoundly studied the history and theory of the subject, has justly remarked[102] the intimate relation which, in the classical ages, existed between the physician and the painter,--the former discovering, supplying, and frequently preparing, the materials used by the latter. This ancient connection was not broken during those ages when almost all knowledge and practice of either medicine or art were limited to the walls of the cloister. The zealous fathers not only worked themselves to the best of their ability, but delighted in training up their younger brethren to perpetuate the credit and revenue derived from their skill, knowledge, and labour, by the monasteries to which they were attached. "Nor was it merely by oral instruction that technical secrets were communicated: the traditional and practical knowledge of the monks was condensed in short manuscript formulæ, sometimes on the subject of the arts alone, but oftener mixed up with chemical and medicinal receipts. These collections, still more heterogeneous in their contents as they received fresh additions from other hands, were afterwards published by secular physicians, under the title of 'Secreta.' The earliest of such manuals serve to show the nature of the researches which were undertaken in the convents for the practical benefit of the arts. Various motives might induce the monks to devote themselves with zeal to such pursuits. It has been seen that their chemical studies were analogous; that their knowledge of the materials fittest for technical purposes, derived as it was from experiments which they had abundant leisure to make, was likely to be of the best kind. Painting was holy in their eyes; and, although the excellence of the work depended on the artist, it was for them to ensure its durability. By a singular combination of circumstances, the employers of the artist, the purchasers of pictures (for such the fraternities were in the majority of cases), were often the manufacturers of the painter's materials. Here, then, was another plain and powerful reason for furnishing the best-prepared colours and vehicles. The cost of the finer pigments was, in almost every case, charged to the employer; but economy could be combined with excellence of quality, when the manufacture was undertaken by the inmates of the convent." All that is asserted in this passage with respect to painting, holds equally good with regard to the materials requisite for the practice of the Art of Illumination; and the same treatises which are illustrative of art generally, almost invariably include specific instructions with regard to the particular branch of it that I am now endeavouring to illustrate.