answers, "the work cannot last, for the solidity of the plaster is impenetrable, and the colours, whether in oil or distemper, cannot pass the surface." This might seem to warrant the inference that absorbent grounds were prepared for oil-painting, but there are proofs enough that resins as well as oil were used with the gesso to make the preparation compact. See Doni, Armenini, &c. This writer, again, does not speak of varnish. These appear to be the chief Venetian and Italian authorities165 of the sixteenth and part of the following century; and although Boschini wrote latest, he appears to have had his information from good sources, and more than once distinctly quotes Palma Giovane.
In all these instances it will be seen that there is no allusion to the immixture of varnishes with the solid colours, except in painting on walls in oil, and that the processes of distemper and oil are always considered as separate arts.166 On the other hand, the prohibition of Boschini cannot be understood to be universal, for it is quite certain that the Venetians varnished their pictures when done.167 After Titian had finished his whole-length portrait of Pope Paul III. it was placed in the sun to be varnished.168 Again, in the archives of the church of S. Niccolo at Treviso a sum is noted (Sept. 21, 1521 ), "per far la vernise da invernisar la Pala dell' altar grando," and the same day a second entry appears of a payment to a painter, "per esser venuto a dar la vernise alla Pala," &c.169 It is to be observed that in both these cases the pictures were varnished as soon as done;170 the varnish employed was perhaps the thin compound of naphtha (oglio di sasso) and melted turpentine (oglio d'abezzo), described by Borghini, and after him by Armenini: the last-named writer remarks that he had seen this varnish used by the best painters in Lombardy, and had heard that it was preferred by Correggio. The consequence of this immediate varnishing may have been that the warm resinous liquid, whatever it was, became united with the colours, and thus at a future time the pigment may have acquired a consistency capable of resisting the ordinary solvents. Not only was the surface of the picture required to be warm, but the varnish was applied soon after it was taken from the fire.171