478 PHILOSOPHICAL TRANSACTIONS. [aNNO 1731. 



shades, and sometimes the out-lines, where they are to appear very sharp, are 

 done with a common graver. Each plate is not completely engraved, but only 

 contrived to take such a portion of the colour as is necessary with the other two 

 plates, to make the picture complete. 



This art of printing consists in 6 articles; viz. 1. To produce any object 

 with 3 colours, and 3 plates. 2. To make the drawings on each of the 3 

 plates, so that they may exactly tally. 3. To engrave the 3 plates, so that they 

 cannot fail to agree. 4. To engrave the 3 plates in an uncommon way, so as 

 that they may produce 3000 and more good prints. 5. To find tlie 3 true pri- 

 mitive material colours, and to prepare them, so as that they may be imprimable, 

 durable, and beautiful. 6. To print the 3 plates, so as that they may agree 

 perfectly in the impression. 



The first of these is the most considerable, comprehending the theoretical 

 part of the invention ; and the other 5 are subservient to bring it into mechani- 

 cal practice; and of such importance, that if any one of tiiem be wanting, no- 

 thing can be executed with success or exactness. Sometimes more than the 3 

 plates may be employed ; viz. when beauty, cheapness, and expedition re- 

 quire it. 



The observation of the compounded colours reflected from two pieces of silk, 

 of different colours, placed near together, first gave him the thought of what 

 the effect of weaving threads of different colours would be, when all the threads 

 were so fine as not to be distinguished from each other at a small distance. 



By the same principles of producing any visible object with a small number 

 of colours, he arrived at the skill of producing in the loom all that the art of 

 painting requires. An art likewise often attempted, but as often abandoned, 

 and declared impossible till now, as well as the other of printing in colours. 

 And probably many improvements may from hence be made in several trades, 

 especially in combing of wool, where the mixing of several colours may be of 

 great use ; but he has not yet had time to apply it to any thing else besides 

 painting, printing, and weaving. 



The colours used in weaving being only superficial, and so differing from both 

 the impalpable and the material colours, and not being to be so closely joined 

 or incorporated together as those, will not of themselves produce a white or 

 black, but only a light cinnamon: therefore, in weaving he has been obliged to 

 make use of white and black threads, besides red, yellow and blue ; and hough 

 he found he was able to imitate any picture with these 5 colours; yet for cheap- 

 ness and expedition, and to add a brightness where it was required, he found it 

 more convenient to make use of several intermediate degrees of colours. 



There are two ways in use at Brussels, and at the goblins in Paris, for making 



