The discovery of mixing oils with the colours for painting, marks a distinct era in the history of the art. It was invented by John Van Eych of Bruges; but the secret of his practice did not travel into Italy till the time of Antonello da Messina, who spent many years in Flanders to study it. Returning to his native country, he stopped at Venice, where he communicated his knowledge to Domenico Venizeano, who carried it to Florence, whence it spread to every part of Europe. It was soon found that colours, when mixed with oil, have a tender softness, which had not been seen in any picture produced before that discovery; and the circumstance of the colours, so prepared, drying with less variation from their appearance when wet, than that which takes place either in distemper or fresco, became the cause that painting in oil was soon universally adopted. It was the custom of the first practitioners in this process, to cover the pannels of their pictures with grounds of thin plaster, which were then prepared for the colours by passing over them, four or five times, a sponge dipped in weak glue. The subject was then traced out accurately, and the colours, mixed up for use in fine linseed or sweet oil, though the latter was preferred, were applied with precision to the respective objects, the artist always working from the lightest tones to the darkest, and his white ground always supporting the brilliancy of his lights, because always thinly painted. The fortunate result of this mode of proceeding is now obvious; for the oil pictures of Raphael, of Leonardo da Vinci, of John de Mabeuge, and others, who painted thinly over a white ground, remain, to this day, with very small variation of their original colour; while many pictures of the Venetian and other schools, which were painted on red, or other grounds prepared by oil colours, have sunk into their foundation, and so far partake of the gloomy colour, that the original subject, in some, is scarcely discernible. After the first period of oil painting, the mode of practice changed considerably. The first painting, or dead colouring of a picture, was now to represent the middle tones of the subject; after which the darks were added, and then the extreme lights; but, as all on this principle were painted on dark-coloured grounds, the consequence has been destruction to the picture. This may be seen particularly in many of the pictures of Guercino, who frequently left the deep red, or black ground of the canvass, for the shadows of his objects.,Rubens attempted to revive the practice of the early Italian oil-painters, by executing all his pictures on white grounds; and they remain, at this day, more brilliant than the works of all his contemporaries who adopted a different system.,The inference from these remarks will be, that a white ground is of great importance in painting, and I wish to bespeak a place in your memories for this principle, as it connects with our subsequent enquiries. In the course of a few years, the first practitioners and admirers of painting in oils, discovered that they had cast off an old and faithful wife for some few defects in her nature, and had taken, without consideration, a beautiful and attractive mistress, who proved at last not to possess so many charms as had been attributed to her. ,It appeared that though the colours in the processes of distemper and fresco changed materially as they dried, that colours, mixed in oils, became darker after they were dry, and not only became darker, but turned to a yellowish colour, inimical to every taint that had a tendency to blue. Hence arose the custom amongst painters of mixing varnish and turpentine with their oils, to dilute and correct the first vehicle; but the inconvenience has not been removed by it.