[455] Digestor. lib. xliii. tit. 11, 12.
[456] Einleitung in die Lehre von den Regalien. Rostock, 1757, 4to, p. 494.
[457] Chronicon Canon, reg. ord. August. capituli Windesemensis; auctore Joh. Buschio. Antv. 1621, 8vo, p. 73.
[458] Schrevelii Harlemum. Lugd. Bat. 1647, 4to, p. 181.
[459] This letter of Fulbert may be found in Maxima Bibliotheca Veterum Patrum. Lugduni 1677, fol. tom. xviii. p. 9.
[460] In Labbei Biblioth. Manuscr. i. p. 132.
[461] Traités de la Police, ii. p. 151.
VERDIGRIS, or SPANISH GREEN.
Respecting the preparation of verdigris, various and in part contradictory opinions have been entertained; and at present, when it is with certainty known, it appears that the process is almost the same as that employed in the time of Theophrastus, Dioscorides, and Vitruvius[462]. At that period, however, every natural green copper salt was comprehended under the name of ærugo. Dioscorides and Pliny say expressly, that a substance of the nature of those stones which yielded copper when melted, was scraped off in the mines of Cyprus; as is still practised in Hungary, where the outer coat of the copper ore is collected in the like manner, and afterwards purified by being washed in water. Another species, according to the account of Dioscorides, was procured from the water of a grotto in the same island; and the most saleable natural verdigris is still collected by a similar method in Hungary. The clear water which runs from old copper-works is put into large vessels, and after some time the green earth falls to the bottom as a sediment.
The artificial ærugo of the ancients, however, was our verdigris, or copper converted into a green salt by acetic acid. To discover the method of procuring this substance could not be difficult, as that metal contracts a green rust oftener than is wished, when in the least exposed to acids. The ancients, for this purpose, used either vessels and plates of copper, or only shavings and filings; and the acid they employed was either the sourest vinegar, or the sour remains left when they made wine; such as grapes become sour, or the stalks and skins after the juice had been pressed from them[463]. Sometimes the copper was only exposed to the vapour of vinegar in close vessels, so that it did not come into immediate contact with the acid; in the same manner as was practised with plates of lead in the time of Theophrastus, when white-lead was made, and as is still practised at present. Sometimes the metal was entirely covered with vinegar, or frequently besprinkled with it, and the green rust was from time to time scraped off; and sometimes copper filings were pounded with vinegar in a copper mortar, till they were changed into the wished-for green salt. This article was frequently adulterated, sometimes with stones, particularly pumice-stone reduced to powder, and sometimes with copperas. The first deception was easily discovered; and to detect the second, nothing was necessary but to roast the verdigris, which betrayed the iron by becoming red; or to add to the verdigris some gall-nut, the astringent ingredients of which united with the oxide of iron of the copperas, and formed a black ink.