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on the colours used in painting by the Ancients. 
substance of exactly the same tint, and of nearly the same 
degree of fusibility, and which, when powdered, produced a 
fine deep sky blue. 
The azure, the red and yellow ochres, and the blacks are 
the colours that seem not to have changed at all, in the ancient 
fresco paintings. The vermilion is darker than recently 
made Dutch cinnabar, and the red lead is inferior in tint to 
that sold in the shops. The greens in general are dull. 
The principle of the composition of the Alexandrian frit is 
perfect; namely, that of embodying the colour in a composi- 
tion resembling stone, so as to prevent the escape of elastic 
matter from it, or the decomposing action of the elements; 
this is a species of artificial lapis lazuli, the colouring matter 
of which is naturally inherent in a hard siliceous stone. 
It is probable that other coloured frits may be made, and it 
is worth trying whether the beautiful purple given by oxide 
of gold, cannot be made useful in painting in a densely tinted 
glass. 
Where frits cannot be employed, metallic combinations 
which are insoluble in water, and which are saturated with 
oxygene or some acid matter, it is evident from the proof of a 
duration of seventeen centuries, are the best pigments. In the 
red ochres the oxide of iron is fully combined with oxygene, 
and in the yellow ochres it is combined with oxygene and 
carbonic acid ; and these colours have not changed. The 
carbonates of copper which contain an oxide and an acid have 
changed very little. 
Massicot and orpiment were probably the least permanent 
amongst the ancient mineral colours. 
Of the colours, the discovery of which is owing to the im- 
MDCCCXV. R 
