Pliny enumerates many resins which were to be dissolved in oil before they could be used as liniments. They are such as flow from the terebinth, larch, lentisk or mastic, and cypress; besides the pine or pitch trees. He also names many gums which might be dissolved in water, or wine, or vinegar, or a mixture of vinegar and wax. Some of these gums he occasionally names as useful to painters; and it is not unreasonable to conclude, that those preparations of them with oil, which would render them so peculiarly convenient as vehicles for colour, or varnishes for preserving pictures, were not overlooked. Such must have been the varnish employed by the Egyptian painters; the brilliant appearance of which is mentioned in Mr. Clift’s letter, printed at the end of the first Essay. There is the authority of Vitruvius for the ancient use of oil in painting doors and other wood-work exposed to the weather. With regard to ships, it appears that their colours--and we know from Homer that they were painted in very ancient times--could not have been laid on with water. I am ignorant how far petroleum, which was known to Herodotus, was calculated to resist weather, or whether any of the resins or juices from the various kinds of fir and pine might, by being mixed with it, render it fit for the purpose. Pliny mentions the substance scraped off the bottoms of ships, as a mixture of pitch and wax, of which a plaster of great efficacy for some kinds of sores was made. It is clear, therefore, that pitch and wax were both used to defend the bottoms and seams of the ships from the effects of the water, and, probably, also to render them smoother, and so to offer less resistance to the waves. But the vermilion-prowed ships must have been painted, and very probably in the encaustic manner; that is, by laying on the colour or the wax to defend it, hot; this would answer the double purpose of shielding the colour, and sending the wax or pitch farther into the substance of the wood, which would thus be better preserved. Indeed, until the general adoption of oil as a vehicle for colour, nothing but the encaustic process could have preserved the figure-heads and the designs on the sterns of the ancient ships during the shortest voyage[267]. It is a pity that Pliny has not left us a more minute account of the process of encaustic painting; but it appears to have been so commonly known and practised in his time, that he has not considered it worth while to describe it particularly. He mentions the doubtfulness of its origin and of its inventor, but speaks of most of the beautiful works of Pausias as having been executed in that manner. In a subsequent passage, writing of vermilion and minium, and of the great luxury at which the Romans of his time had arrived in fine colours, he mentions that walls coloured with those expensive pigments were apt to blacken unless defended by a varnish of wax, for which he gives the following recipe:--