330 PHILOSOPHICAL TRANSACTIONS. [anNO IJSg. 



but as the chalk did not absorb the wax, the picture fell from the board and left 

 it quite bare. 



Exper. 3. — He mixed 3 parts white wax, and one part white resin, hoping the 

 tenacity of the resin might preserve the picture. This was laid on a board 

 heated with a brush, as in the former ; and the ground was chalk, prepared as 

 before. This was placed horizontally on an ironing box, charged with a hot 

 heater, shifting it from time to time, that the wax and resin might penetrate 

 the chalk ; and hoping from this position that the ground bloated by melting 

 the wax, would subside into its proper place : but this, like the other, came 

 from the board, and would not at all adhere. 



Exper. A. — Prepared chalk 4 drams, white wax, white resin, of each a dram, 

 burnt alabaster half a dram, were all powdered together and sifted, mixed with 

 spirit of molosses instead of water, and put for a ground on a board smeared 

 with wax and resin, as in Exp. 3. This was also placed horizontally on a box- 

 iron, as the former : the picture blistered and was cracked all over ; and though 

 removed from the box-iron to an oven moderately heated, in the same horizontal 

 position, it would not subside, nor become smooth. When cold, he took an 

 iron spatula made warm, and moved it gently over the surface of the picture, as 

 if to spread a plaster. This succeeded so well, as to reduce the surface to a to- 

 lerable degree of smoothness: but as the ground was broken off in many places, 

 he repaired it with flake white, mixed up with the yolk of an &gg and milk, and 

 repainted it with molosses spirit, instead of water ; and then put it into an oven 

 with a moderate degree of heat. In this he found the colours fixed, but darker 

 than when it was first painted ; and it would bear being washed with water, not 

 rubbed with a wet cloth. 



Exper. 5 . — A board that had been used in a former experiment, was smeared 

 with wax and resin, of each equal parts ; was wetted with molosses spirit, to make 

 whitening (or Spanish white) mixed with gum-water adhere. This, when dry, 

 was scraped with a knife, to make it equally thick in all places. It was put into 

 a warm oven, to make the varnish incorporate partly with the whitening before 

 it was painted ; and it had only a small degree of heat : water only was used to 

 mix the colours. This was again put into an oven with a greater degree of heat; 

 but it flaked off from the board. 



Exper. 6. — Having miscarried in these trials, he took a new board, planed 

 smooth, but not polished, either with a fish-skin or rushes: he warmed it, and 

 smeared it with wax only ; then took cimolia (tobacco-pipe clay) divested of its 

 sand, by being dissolved in water and poured oflT, leaving the coarse heavy parts 

 behind. After this was dried and powdered, he mixed it with a small quantity 

 of the yolk of an egg and cow's milk, and made a ground with this on the 

 waxed board. When the ground was near dry, he smoothed it with a pallet- 



