Permanent Colours of Opake Bodies. i6g 



are obfcured, and bounded within the narrow 

 limits of accidental obfervation. 



The knowledge of the optical properties of 

 colouring matters, is alfo eficntially requifue to 

 their due preparation and vfc. As the pravflice of 

 dying, in its prefcnc ftate, is not regulated by 

 any fcientific rules, it is fcldom improved by the 

 introduction of new proceflcs : and the methods 

 of varying the ufes ot the materials, which are 

 already known, are rarely afcertained without 

 repeated trials. 



. All the operations of the art, excepting only 

 a few which have arifen from accidental difco- 

 veries, owe their origin to remote ages. 



We learn from the teftimony of the facrcd 

 writers, as well as of the later hiftorians, that the 

 Indians, Egyptians, Phoenicians, and other anci- 

 ent nations, excelled in the art of dying. From 

 the accounts, which are delivered down to us, of 

 the colouring materials which they ufed, and of 

 ihe clothes which were dvcd with them, we find 

 evident proofs, that they were acquainted with 

 the principles, as well as the praftice, of the art. 



The ancients did not attribute a refleflive 

 power to the colouring matter j but held, that the 

 dyed clothes refleftcd lefs light, in proportion 

 as they were more copioufly ftored with tinging 

 particles. They eftimated the richnefs and in- 

 tenfencfs of the dye, by its approach to blacknefs. 



Pliny, who has recorded many curious circum- 

 ftances relative to the arts, defcribes indigo, when 



undiluted. 



