[ 5 ° J 
pofed to the open air in a very foggy night. In the 
morning the board was feemingly wet through, and 
the water ran off the pi&ure. This was buffered to 
dry without wiping ; and the pidure had not buffered 
at all from the fmoke or the dew, either in the 
ground or the colours : but when dry, by rubbing it, 
firff with a foft cloth, and afterwards with a brufh, it 
recovered its former glofs. 
Sufpeding that fome tallow might have been 
mixed with the white wax I had ufed, which might 
caufe the colours to come off on being rubbed with 
a wet cloth, I took yellow wax which had been 
melted from the honeycomb in a private family, 
and confequently not at all adulterated ; to three 
parts of this I added one part refin, and melted 
them together. 
Experiment IX. 
Spanifh white, mixed with frfh glew, was put for 
a ground on a board, and painted with water colours 
only. The board was made warm ; and then the 
wax and refin were put on with a brufh, and kept 
clofe to the fire till the picture had imbibed all the 
varnifh, and looked dry. When it was cold, I rub- 
bed it firff with a linen cloth, and then poliffied it 
with an hard brufh. 
In thefe experiments I found great difficulties with 
regard to colours > many water colours being made 
from the juices of plants, have fome degree of an 
acid in them ; and thefe, when painted on an alka- 
line ground, as chalk, whitening, cimolia , and plaifter, 
are, totally changed their colours, and from green 
became 
