Although we would here willingly end the discussion as to the discovery, we feel ourselves irresistibly led by the importance of the subject to make a few observations, and perhaps throw out a few hints, presuming that they are nothing more than hints, which suggest themselves upon paying some little attention to the actual words of Vasari; and this we do solely with regard to vehicles. Why, we should ask, did Van Eyck dry his picture in the sun, and which seems to have been the practice? As far as we know the nature of gums, there is no difficulty in their drying, without the necessity of resorting to any injurious practice. Were these gums in any degree mixed with undrying substances? Why does Vasari say "che secca non teme acqua"--"which, dry, does not fear water?" Why does he mention water at all? for, supposing that he knew of oil-painting without these "altre sue misture," there would appear to be no occasion that he should mention, as a distinct property of this new vehicle, that which was common with that and the older practice. Here a suggestion seems to let in a glimmer of light. Did he convert these oils into a soap, which, when dry, was no longer soluble in water? Will this be the case with saponaceous oils? Unquestionably. One of the objections made by Lanzi to the changes from the good old method was, as when he speaks of Maria Crespi, that the paint was common and _oily_, and elsewhere complains of "oily appearances." The "colori oleosi" is perfectly descriptive, too, of our modern paint, notwithstanding that our painters try in vain to disguise the "oily" appearance by the admixture of varnishes, and that not a new practice, as we find from Cennino, but one rejected. But can oil be deprived of this appearance? We presume it was deprived of this quality by that process by which, when dry, it did not "fear water"--"secca non teme acqua." Oils are rendered saponaceous by alkalis. We mentioned in former papers experiments of our scientific friend, P. Rainier, M.D. of the Albany, and his use of borax with the oil. The borax he vitrified; and it was because the paint mixed with this oil and borax vitrified also, after the manner of the paint of the old masters, he so used it; but nothing occurred to him about water. We suggested that if this, his medium, resembled the old, it was probably miscible with water, as water would seem to have been introduced into the Venetian practice. Upon this we tried it, and found we could at pleasure dip the brush in this medium, or in water, and then into the paint, and work with great facility, the greater use of the water giving that _crumbly_ appearance so often perceptible in the Venetian school; and this effect we found might be increased or omitted at pleasure. And this medium, made by mixing water with the oil through the agency of borax, when dry might be washed even with warm water with perfect impunity. _When dry it did not fear water_;