o53 Experiments and Observations 



some of the mouldings detaclied from the ceilings of the cham- 

 bers in the baths of Titus: and the walls of one chamber between 

 the compartments of red marble, boar proofs of having been co- 

 vered with this frit, and retain a considerabk quantity of it. 



There is every reason to believe that this is the colour de- 

 scribed by Theophractus as discovered by un Egyptian king * ; 

 and of which the manufactory is s^iid to have been anciently 

 established at Aler^andria. 



Vitruvius spsalis of it, under the name of cceridet/mf, as the 

 colour used commonly in paintiisg c.lKimbcrs, and states, that it 

 was made in his time at Piizzuoli, where the method of fabrica- 

 ting it was bionght from Egypt by Vestorius : he gives the me- 

 thod of preparing it by heating strongly together sand, fios 

 Jiitri I, and filings of copper. 



Pliny mentions other blues, which he calls species of satid 

 {arence) from the mines of Egypt, Scythia, and Cyprus. These 

 natural blues, there is reason to believe, were different prepara- 

 tions of lapis lazuli, and of the blue carbonates and arseniates of 

 copper. '' 



Both Pliny and Vitruvius speak of the Indian blue, which the 

 firat author states to be combustiblej and which was evidently a 

 fcpecies of idigo. 



I have examined several blues in the fragments of fresco paint- 

 ing from the ruins near the monument of Caius Cestjus. In a 

 deep blue approaching in tint to indigo, I found a little carbonate 

 of cojjper, but the basis of this colour was the hit before de- 

 scribed. 



The blues in the Nozze Aldo])rrmdine, from their resisting the 

 action of acids, and from the effects of fire,'! am i'-.chned to 

 consider as composed of the Alexandrian or Puzzuoli b'';e. 



In an excavation made at Por.ipeii, in May ISM, at which I 

 was present, a suklU pot containing a pale blue colour was dug 

 up, which the exalted personage, by whose command the exca- 

 vation was made, was so good as "to put into my hands. It 

 proved to be a mixture of carboiuile of lime with the Alcxandrifin 

 frit§. 



Vitruvius state;, that the ancients had a mode of imitating the 

 Indian blue or indigo, by mixing the powder of tl'.c glass called 

 by the Greeks vu:\oc, with selinnsian "crctii" or annularian 

 '' crcta," which was wliile clay or chalk mixed with stained 

 glttbs ; the same practice is likewise referred to by Pliny. 



* De LRpidihiis, sect, scviji. f Lib. vii. cap. 11. 



t Tiiis idenli-.ies fhe nitrum of the .-.ncitnls with carbonate of s-oda. 



§ Tills probabl) is t.'ie same colour as t!i;it examined liy M. Cliaptal. TTc 

 djd not besirrli ju u for alkali, or iLcrc ib every reason to !5Ui)j)osc he would 

 Iwve I'ound :,oda. 



There 



