13 



prepared from shell-fish is in a broken vase in the baths of Titus, 

 containing a substance which at the surface has become of a cream 

 colour, but in the interior has a lustre approaching to that of car- 

 mine. The colouring matter of this substance was found to be com- 

 bustible, constituting about one thirtieth part of its weight, the re- 

 mainder being a compound of siliceous, aluminous, and calcareous 

 earths. It may, therefore, be regarded as a lake ; but it would be 

 very difficult, if not impossible, at this distance of time, to determine 

 whether it be of animal or vegetable origin. In either case its du- 

 rability, even in the interior of the mass, is a very curious circum- 

 stance, although the part exposed to the air has suffered the changes 

 to which such colours have been too often proved to be liable, and 

 accordingly no traces of it remain in any of the ancient fresco paint- 

 ings. 



All the blacks observable in the baths of Titus or elsewhere ac- 

 cord with the descriptions given by ancient authors, who speak of 

 them as carbonaceous substances, obtained either as common char- 

 coal or as soots of woods or resins. 



The browns are sometimes mere oxides of iron or ochres, and 

 sometimes mixtures of the oxides of iron and manganese ; and it ap- 

 pears that the Romans had some knowledge of the properties pecu- 

 liar to the latter substance, as Sir Humphry Davy has analysed two 

 specimens of ancient Roman purple glass, both of which were tinged 

 with manganese. 



Among the whites of the ancient paintings, the author was un- 

 able to discover any ceruse, although it is known to have been in 

 common use on the authority of Theophrastus, Vitruvius, and Pliny. 

 The'whites found are in general carbonate of lime, or fine white clays. 



The ground to which the colours are applied in the ancient fresco 

 paintings, is precisely such as is described by Vitruvius, powdered 

 marble cemented by lime, highly polished and beautifully white. 

 With regard to the mode in which their colours were applied, Vi- 

 truvius and Pliny agree as to the employment of wax in encaustic 

 painting, which was subsequently liquefied by heat so as to give a 

 varnish to the painting. But the author has not in any instance 

 been able to detect the presence of wax, nor yet of any animal or 

 vegetable gluten, in any of the fresco paintings, or even in the pot 

 of colours found at Pompeii. 



From the facts above stated, it appears that the Greek and Roman 

 painters had the advantage over the great Italian masters, since the 

 revival of civilization, in two of their colours, the Tyrian purple and 

 the Egyptian azure, although the latter may easily and cheaply be 

 imitated ; for if a mixture of about fifteen parts of soda, twenty parts 

 of powdered flint, and three parts of copper filings, be strongly heat- 

 ed together for about two hours, a frit is produced extremely similar 

 in appearance and degree of fusibility to the ancient blue frit. 



