196 PLINt's ]!^ATUPtAL HISTOKT. [Book XXXIY. 



in numerous ways. Sometimes it is detached already formed, 

 from the mineral from which copper is smelted : and some- 

 times it is made by piercing holes in white copper, and sus- 

 pending it over strong vinegar in casks, which are closed with 

 covers ; it being much superior if scales of copper are used for 

 the purpose. Some persons plunge vessels themselves, made 

 of white copper, into earthen pots filled with vinegar, and 

 scrape them at the end of ten days. Others, again, cover the 

 vessels with husks of grapes,^ and scrape them in the same 

 way, at the end of ten days. Others sprinkle vinegar upon 

 copper filings, and stir them frequently with a spatula in the 

 course of the day, until they are completely dissolved. Others 

 prefer triturating these filings with vinegar in a brazen 

 mortar : but the most expeditious method of all is to add to 

 the vinegar shavings of coronet copper.^ Rhodian verdigris, 

 more particularly, is adulterated with pounded marble ; some 

 persons use pumice-stone or gum. 



The adulteration, however, which is the most difficult to 

 detect, is made with copperas;^ the other sophistications 

 being detected by the crackling of the substance when bitten 

 with the teeth. The best mode of testing it is by using an 

 iron fire-shovel; for when thus subjected to the fire, if pure, 

 the verdigris retains its colour, but if mixed with copperas, it 

 becomes red. The fraud may also be detected by using a leaf 

 of papyrus, which has been steeped in an infusion of nut-galls ; 

 for it becomes black immediately upon the genuine verdigris 

 being applied. It may also be detected by the eye ; the green 

 colour being unpleasant to the sight. But whether it is pure 

 or adulterated, the best method is first to wash and dry it, and 

 then to burn it in a new earthen vessel, turning it over until 

 it is reduced to an ash ;' after which it is pounded and put by 

 for use. Some persons calcine it in raw earthen vessels, until 

 the earthenware becomes thoroughly baked : others again add 

 to it male frankincense.^ Verdigris is washed, too, in the same 

 manner as cadmia. 



* According to Brotero, tliis is the process generally adopted in France, 

 in preference to tlie employment of vinegar in a pure state, — B. 



^ The form of copper whicli was termed " coronariura" has been already 

 described in Cbapter 22. — B. 



® " Atramento sutorio." " Shoemakers' black." See Chapters 27 and 

 22 of this Book. 



■^ Until it assumes an ashy colour, Dioscorides says. — B. 



8 See B. xii. oc. 30, 32. 



