148 SYSTEM. 



representations, and the best will be those which show us the 

 individual with untouched beard and hair. 



As to colour, we must refer as much as possible to oil-paint- 

 ing. In fact, the colour of the human skin, as we have formerly 

 said,* is, in reality, a complex visual impression; all the 

 coloured rays (we employ the term here in the conventional 

 sense given to it in physics) which emanate from the skin, and 

 which strike the eye of the observer, are not formed by the 

 same plane surface ; they arise from the more or less profound 

 parts seen by transparency, through a more or less diaphanous 

 medium, more or less favourable for the emission of these rays. 

 Hence results, as regards the eye, a special sensation, and as 

 regards the mind, a special notion, which we explain in the 

 arts by the word transparency or diaphaneity. 



Now, this kind of sensation will not be reproduced by the 

 artist unless he employs certain processes recalling to the 

 mind those of nature itself. This is not the case with water- 

 colour painting. The colouring matter, reduced to extremely 

 fine particles, is applied, it is true, in a transparent vehicle 

 water; but this, destined to evaporate almost immediately, 

 leaves the colour on the surface of the paper, stretched into an 

 extremely fine layer, without appreciable thickness. We per- 

 ceive from this the radical imperfection of water-colour for 

 portraiture, and the impossibility of rendering by such means, 

 at least with truth, the effect of skin colours. Oil painting 

 offers far better resources, and here is the secret of its in- 

 comparable superiority. The colouring matter, diluted by the 

 oil, remains suspended as before in its transparent medium 

 when the painting is dry ; so that the luminous rays, in order 

 to arrive at the eye, start from the surface of the paint as well 

 as from its interior substance. We find exactly the same 

 process in nature ; an impalpable powder, like the pigmentary 

 granulations, or the globules of blood in the capillaries of the 

 skin, is spread over a diaphanous substance. 



We may now understand the advantage of such a process in 

 anthropological iconography. We must, indeed, almost give 



* Des Colorations de I'epiderme, 4to, Paris, 1864. 



