124 Humphry Davy’s experiments and observations , &c. 
the oil and the canvas are vegetable materials, and liable to 
decomposition, and the last is less durable than even the wood 
on which the Greek artists painted their celebrated pictures. 
It is unfortunate that the materials for receiving those works 
which are worthy of passing down to posterity as eternal 
monuments of genius, taste, and industry, are not imperishable 
marble* or stone : and that frits, or unalterable metallic com- 
binations, have not been the only pigments employed by great 
artists ; and that their varnishes have not been sought for 
amongst the transparent combinations of the earths with 
water, or amongst the crystalline transparent compounds un- 
alterable in the atmosphere.-f 
* Copper, it is evident, from the specimens in the ruins of Pompeii, is a very 
perishable material, and, therefore, even enamels made on copper will yield to time. 
Canvas, by being impregnated with bitumen, is rendered much more durable, as is 
evident from the duration of the linen impregnated with bitumen and aspbaltum used 
for infolding the Egyptian mummies. 
f The artificial hydrat of alumina will probably be found to be a substance of this 
kind : possibly the solution of boracic acid in alcohol will form a varnish.— The so- 
lution of sulphur in alcohol is likewise worthy of an experiment. Many other similar 
combinations might be named. 
fLomv, January i\tb, 1815. 
