There are miniatures by Cosway which are of pre-eminent beauty, so lightly and with such exquisite skill are they floated upon the ivory. The quality of the material had, of course, an intimate connection with the art of the painter. The seventeenth-century artists knew nothing of the brilliant surface of ivory, although it is possible that one at least of them had an inkling that a more luminous material than vellum, cardboard, or chicken-skin, could be found. There are two miniatures in existence, one of which is in the possession of the author of these pages, the work of Cooper, which are not painted on any of the materials usually adopted by him. This latter is painted on what was at first thought to be a piece of ivory, but microscopic investigation has revealed the fact that it is polished mutton-bone, and the painter has so altered his technique to adapt it to this curious experiment, that for the first moment one would hardly believe the miniature to be by Cooper at all. Its pedigree is, however, unassailable, and a closer investigation reveals many of the master's characteristics, but it is painted with a very fine brush, quite different to the usual broad, full sweep of his work, and it stands out as an interesting experiment on the part of the great painter, who was searching for some material more suitable for a particular style of work. Ivory was not employed until the time of William III., and it seems probable that one of the Lens family was the first to make use of it; but, once adopted, its use became very general, and in the prolific period of the eighteenth century, almost universal. Cosway is said to have experimented in enamel, and certainly one enamel portrait, with his initials, is in existence. He drew very skilfully on paper, and a few of his miniatures are on that material. One of his works, signed and dated, is on silk, but all these were only experiments, and the greater number of his miniatures are on ivory, which material lends itself perfectly to his craft. In our opinion the finest miniature Cosway ever produced was his unfinished sketch of _Madame du Barry_, one of the greatest treasures of Mr. Pierpont Morgan's collection, and by his kind permission illustrated here in monotone (Plate XII.). It was painted in 1791 on the occasion when Madame du Barry came over to England to recover her jewels, and on her third visit to this country in that year. From this portrait a stipple engraving was made by Condé in 1794, but the miniature itself came into the possession of the Vernons, having belonged to a Miss Caroline Vernon who was maid of honour to Queen Charlotte. It was sold in London in 1902, when it passed to its present owner, and in grace, sweetness, and fascination, is unrivalled, even amongst his wonderful treasures.