BOOK XXXIII. XL. I2I-XLI. 123 



it keeps its colour. I find that it is also adulterated 

 with lime, and this can be detected in a similar way 

 with a sheet of red-hot iron if there is no gold avail- 

 able. A surface painted with cinnabar is damaged 

 by the action of sunlight and moonlight. The way 

 to prevent this is to let the wall dry and then to coat 

 it with Punic wax melted with oHve oil and apphed 

 by means of brushes of bristles while it is still hot, 

 and then this wax coating must be again heated by 

 bringing near to it burning charcoal made of plant- 

 galls, till it exudes drops of perspiration, and after- 

 wards smoothed down with waxed rollers and then 

 with clean linen cloths, in the way in which marble 

 is given a shine. Persons poHshing cinnabar in 

 workshops tie on their face loose masks of bladder- 

 skin, to prevent their inhaHng the dust in breathing, 

 which is very pernicious, and nevertheless to allow 

 them to see over the bladders. Cinnabar is also used 

 in writing books, and it makes a brighter lettering 

 for inscriptions on a waH or on marble even in tombs. 

 XLI. Of secondary importance « is the fact that 

 experience has also discovered a way of getting 

 hydrargyrum or artiiicial quicksilver as a substitute 

 for real quicksilver ; we postponed the description 

 of this a Httle previously. It is made in two ways, §§ g4, 100. 

 by pounding red-lead in vinegar with a copper 

 pestle in a copper mortar, or it is put in an iron shell 

 in flat earthenware pans, and covered with a convex 

 Hd smeared on with clay, and then a fire is Ht under 

 the pans and kept constantly burning by means of 

 bellows, and so the surface moisture (with the colour 

 of silver and the fluidity of water) which forms on the 

 Hd is wiped off it. This moisture is also easily 

 divided into drops and rains down freely with sHppery 



93 



