_Atramentum_ was obviously from Pliny’s account of it _lamp-black_. He mentions ivory-black as an invention of Apelles: it was called _elephantinum_. There was a native atramentum, which had the colour of sulphur, and got a black colour artificially. It is not unlikely that it contained sulphate of iron, and that it got its black colour from the admixture of some astringent substance. The ink of the ancients was lamp-black mixed with water, containing gum or glue dissolved in it. _Atramentum indicum_ was the same as our _China ink_. The _purpurissum_ was a high-priced pigment. It was made by putting _creta argentaria_ (a species of white clay) into the caldrons containing the ingredients for dying purple. The creta imbibed the purple colour and became _purpurissum_. The first portion of _creta_ put in constituted the finest and highest-priced pigment. The portions put in afterwards became successively worse, and were, of consequence lower priced. We see, from this description, that it was a lake similar to our modern cochineal lakes.[71] [71] Plinii Hist. Nat. xxxv. 6. That the purpurissum indicum was indigo is obvious from the statement of Pliny, that when thrown upon hot coals it gives out a beautiful purple flame. This constitutes the character of indigo. Its price in Pliny’s time was ten denarii, or six shillings and five-pence halfpenny the Roman pound; which is equivalent to 8_s._ 7⅓_d._ the avoirdupois. Though few or none of the ancient pictures have been preserved, yet several specimens of the colours used by them still remain in Rome and in the ruins of Herculaneum. Among others the fresco paintings, in the baths of Titus, still remain; and as these were made for a Roman emperor, we might expect to find the most beautiful and costly colours employed in them. These paints, and some others, were examined by Sir Humphrey Davy, in 1813, while he was in Rome. From his researches we derive some pretty accurate information respecting the colours employed by the painters of Greece and Rome. 1. _Red paints._ Three different kinds of red were found in a chamber opened in 1811, in the baths of Titus, namely, a bright orange red, a dull red, and a brown red. The bright orange red was _minium_, or _red lead_; the other two were merely two varieties of iron ochres. Another still brighter red was observed on the walls; it proved, on examination, to be _vermilion_ or _cinnabar_.