It is the opinion of the author of "Materials for a History," &c., that the Van Eycks did not so much invent as improve; it was therefore most desirable to ascertain what was previously ready to their hands to be improved. And as to the improvement, that was perhaps really less than has been supposed, the application being the novelty. Oleo-resinous varnishes had before been in use, even from a very early period; but the admixture of these with the pigments was the great step in advance, and it may be inferred that the method of rendering these oleo-resinous vehicles colourless, or nearly so, was the great invention of John Van Eyck. Drying oil was well known to the ancients, that is before the Christian era. "Dioscorides, whose works were familiar to medieval writers on medicine, is supposed to have lived in the age of Augustus. He mentions two drying oils; walnut-oil and poppy-oil. The principal materials employed in modern oil painting were at least ready for the artist, and waited only for a Van Eyck,--in the age of Ludius[11] and the painters of Pompeii." We will not attempt further to pursue the history of oil painting to the time of the Van Eycks; suffice it to say, that a recipe of Theophilus, a monk of the twelfth century, furnishes materials--an oleo-resinous vehicle generally used after the time of Van Eyck--and that the improvement by Van Eyck was the substituting amber for the sandarach of Theophilus. The work of Theophilus has recently appeared, translated by Mr Hendrie from the Latin, and forms a very valuable addition to the painter's library, as well as to that of the curious and scientific, in general. The artist will find in Mr Hendrie's preface, the information he will be most desirous to possess. He strongly insists upon amber varnish as being the real vehicle or discovery of Van Eyck, and lays much stress upon a certain distilled oil as a diluent. He says:-- "Amber varnish, and probably other thick oil varnishes, would be equally benefitted, thinned with this distilled oil. It dries without a pellicle when mixed with colours. Colours used for finishing a picture, such as in the light for solid painting, or glazing for colour and shadows, are rendered very pure and without the slightest appearance of a skin, although it may be plentifully used. It dries much more slowly than any other distilled oil, and hence its great value, as it allows the artist as much time as he requires, in order to blend his colours and finish his work. In conjunction with amber varnish, it forms a vehicle which leaves nothing to be desired, and which doubtless was the vehicle of Van Eyck, and in many instances of the Venetian masters, and of Correggio; the different modes of painting necessarily producing the varied appearances of the different schools and masters."