35^ Ejiperiments ami OLservationi 



II. Of the Red Colours of the Ancients. 



Amongst the substances found in a large eartlien vase fille«i 

 with mixtures of different colours with clay and chalk, found 

 about t\^•o years ago in a chamber at that time opened in the 

 baths of Titus, are three different kinds of red ; one bright and 

 approaching to orange, another dull red, a third a purplish red*. 

 On exposing the bright red to the flame of alcohol, it became 

 darker red ; and on increasing the 'heat by a blow-pipe, it fused 

 into a mass having the appearance of litharge, and which was 

 proved to be this substance by the action of sulphuric and mu- 

 riatic acids. This colour is consequently minium, or the red 

 oxide of lead. 



On exposing the dull red to heat, it became black, but on 

 cooling recovered its former tint. When heated in a glass tube 

 it afforded no volatile matter condensible by cold but water. 

 Acted on by muriatic acid, it rendered it yellow ; and the acid, 

 after being heated upon it, yielded an orange- coloured precipitate 

 to ammonia. When fused with hydrate of potassa, the colour 

 rendered it yellow ; and the mixture acted on by nitric acid af- 

 forded silica and orange oxide of iron. It is evident from these 

 results that the dull red colour is an iron ochre. 



The purplish red submitted to experiments, exhibited similar 

 phenomena, and proved to be an ochre of a different tint. 



In examining the fresco paintings in the baths of Titus, 1 

 found that these colours had been ail of them used, the ochres 

 particularly, in the shades of the figures, and the minium in the 

 crnaraents on the borders. 



I found another red on the walls, of a tint different from those 

 in the vase and much brighter, and which had been employed 

 in various apartments, and formed tlie basis of the colouring of 

 the niche and other parts of the chamber in which the Laocoon 

 is said to have been found. On scraping a little of this colour 

 from the v/all, and submitting it to chemical tests, it proved to 

 be vermilion or cinnabar, and on heating it with iron filings, 

 running quicksilver was procured from it. 



I found the same colour on some fragments of ancient stucco 

 in a vineyard near the pyramidal monument of Caius Ctstius. 



In the Nozze Aldobrandine, the reds are all ochres. I tried 

 on these reds the action of acids, of alkalies, and of chlorine, 

 , but could discover no traces either of minium or vermilion in 

 this picture. 



Minium was known to the Greeks under the name of a-avla- 

 ^'^yji t> and to the Romans under that of cerussa tista. It is said, 



* Nearly of die samo tint as prussiatc of cojipcr. 

 t Diascoricks, lib. v. I'J','. 



