as Objens of the Art of Dying, ^c. 363 



Having thus confidered the natures of the 

 different fubjefts of dying, and the various 

 preparations neceffary for fitting them for the 

 reception of colouring naatter, in general. Let 

 us next proceed to fome defcriprion of the 

 colouring fubftances which are employed in 



dying. 



Thefe are divided into two clafles, viz. thofe 

 which are themfelves poffeffed of colour ; and 

 thofe, which poffeffing no colour in themfelves, 

 alter the power of the former to tranfmit the 

 various rays of light; thereby enabling them to 

 exhibit colours different from thofe which they 

 would naturally exhibit. 



When I fay that fubftances do themfelves pof- 

 fcfs colour, I only mean, that they polTefs the 

 power of tranfmitting particular rays of light ; fo 

 as to produce, by the aftion of thefe rays on the 

 retina, the idea of certain colours. 



Though the primitive colours, into which a 

 ray of light may be divided, are fcven ; yet the 

 original ""colours produced by dyers are no more 

 than five, viz. blue, red, yellow, brown and 

 black. From thefe, perhaps, the two laft may 

 be excluded as compounds. All the other Ihades. 

 of various denominations, are formed by dif- 

 ferent combinations of thefe original colours. 



The fubftances which do, themfelves, contain 

 colouring matter, and are ufed in dying, are 

 chiefly of the vegetable, fome of the animal, 

 and, in a few inftances, of the mineral kingdom. 

 - ' The 



