VOL. LI.] PHILOSOPHICAL TRANSACTIONS. 331 



knife, and washed with milk and egg where he had occasion to make it smooth 

 and even : when dry he painted it, mixing the colours with common water ; this 

 on being placed horizontally in an oven, only warm enough to melt the wax, 

 flaked from the board ; but held so much better together than any of the former, 

 that he pasted part of it on paper. 



Exper. 7. — Flake white mixed with egg and milk, crumbled all to pieces in 

 the oven when put on the waxed board, as in the last experiment. The bad 

 success which had attended all the former experiments, led him to consider of 

 what use J^he wax was in this kind of painting ; and it occurred that it was only 

 as a varnish to preserve the colours from fading. In order to try this, 



Exper. 8. — He took what the bricklayers call fine stuff, or putty ; to this he 

 added a small quantity of burnt alabaster to make it dry : this it soon did in the 

 open air ; but before he put on any colours, he dried it gently by the fire, lest 

 the colours should run. When it was painted, he warmed it gradually by the 

 fire, to prevent the ground from cracking, till it was very hot. He then took 

 white wax 3 parts, white resin one part, melted them in an earthen pipkin, and 

 with a brush spread them all over the painted board, and kept it close to the fire 

 in a perpendicular situation, that what wax and resin the plaster would not ab- 

 sorb might drop off. When cold, he found the colours were not altered, 

 either from the heat of the fire or passing the brush over them. He then rubbed 

 it with a soft linen cloth, and thus procured a kind of gloss, which he after- 

 wards increased by rubbing it with a hard brush ; which was so far from scratch- 

 ing or leaving any marks on the picture, that it became more smooth and po- 

 lished by it. 



After he had made all the foregoing experiments, in conversation with Dr. 

 Kidby, who told him that there was a passage in Vitruvius de Architectura re- 

 lative to that kind of painting ; and which, when translated, runs thus : "- But 

 if any one is more wary, and would have the polishing [painting] with vermilion 

 hold its colour, when the wall is painted and dry, let him take Carthaginian 

 [Barbary] wax, melted with a little oil, and rub it on the wall with a hair pen- 

 cil ; and afterwards let him put live coals into an iron vessel (chafing dish,) and 

 hold it close to the wax, when the wall, by being heated, begins to sweat ; 

 then let it be made smooth : afterwards let him rub it with a candle and clean 

 linen rags, in the same manner as they do the naked marble statues. This the 

 Greeks call xauo-i?. The coat of Carthaginian wax, thus put on is so strong, that 

 it neither suffers the moon by night, nor the sun-beams by day to destroy the 

 colour." Being satisfied, from this passage in Vitruvius, that the manner of 

 using wax in Exper. 8 was right, Mr. C. was now to find if the wax-varnish, 

 thus burnt into the picture would bear washing : but here he was a little disap- 

 pointed ; for rubbing one corner with a wet linen cloth, some of the colour 



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