GREEN COLOUR FOR FOLIAGE. 79 



the former are generally considered as being flat 

 and flaky, whereas those of the latter are tubular 

 and round : this conformation renders silk so soft to 

 the touch, and refracting more perfectly the rays 

 of light, occasions much of its lustre, and the bril- 

 liancy of its hues. Perhaps we have no art or trade 

 less confined within the trammels of formulae than 

 that of the dyer ; every professor appearing to have 

 his own methods of acquiring particular tints and 

 shades, guided often in his proportions by that 

 mutable sense, the taste, and regulating the tempe- 

 rature of his compositions, not by the thermometer, 

 but by the feeling of the hand ; and so capricious 

 are these tests, so different the sensations of the 

 operator, or the variable influences of solar light, 

 that success on one day does not ensure a similar 

 result on another. 



Colour is probably only reflected light ; but by 

 what means the absorption of oxygen increases the 

 lustre is not quite obvious yet the power of the 

 sun's rays, in augmenting the intensity of the hues 

 of many things, is well known : there is an admir- 

 able green colour for foliage, to be obtained by the 

 union of the light Prussian blue with the dark 

 gamboge ; but I could never acquire this clear and 

 lustrous, without compounding it in the light of 

 the sun. As the young artist will find this a most 

 useful pigment, I may in addition say, that a small 

 bit of the light Prussian, with three or four times 



