COLOURING MATTER AND PRINCIPLES OF DTING. 



Id 



required, to the works they are designed 

 for; eight ends sufficing for ribands ; and 

 velvets requiring no less than fourteen. 

 ( To be continued.) 



COLOURING MATTER AND PRINCPLES OF 

 DTING. 



The substances commonly employed for 

 clothing may be reduced to four, namely, 

 wool, silk, cotton and linen. 



Permanent alterations in the colour of 

 cloth can only be induced two ways; ei- 

 ther by producing a chemical change in 

 the cloth, or by covering its fibres with 

 some substances which possess the wish- 

 ed for colour. — Recourse can seldom or 

 never be had to the first method, because 

 it is hardly possible to produce a chemical 

 change in the fibres of cloth, without 

 spoiling its texture and rendering it use- 

 less. The dyer, therefore when he wishes 

 to give a new colour to a cloth, has al- 

 ways recourse to the second method. 



The substances employed for this pur- 

 pose are colouring matters, or dye-stuffs. 

 They are for the most part extracted from 

 animal and vegetable substances, and have 

 usually the colour which they are to give 

 to the cloth. 



Since the particles of colouring matter, 

 with which cloth when dyed is covered 

 are transparent, it follows that all the 

 light reflected from dyed cloth, must be 

 reflected, not by the dye-stuff itself, but 

 by the fibres of cloth below the dye-stuff. 

 The colour therefore does not depend up- 

 on the dye alone, but also on the previous 

 colour of the cloth. If the cloth be black, 

 it is clear that we cannot dye it any other 

 colour whatever; because as no light in that 

 case is reflected, none can be transmitted, 

 whatever dye-stuff we employ. If the 

 cloth be red, blue, or yellow, we could 

 not dye it any colour except black; be- 

 cause, as only red, or blue, or yellow rays 

 are reflected, no other could be transmit- 

 ted. Hence the importance of a fine white 

 colour when'cloth is'to receive bright dyes. 

 It then reflects all the rays in abundance, 

 and therefore any colour may be given, 

 by covering it with a dye-stuff which 

 transmits only some particular rays. If 

 the colouring matters were merely spread 

 over the surface of the fibres of cloth by 

 the dyer, the colours produced might be 

 very bright, but they could not be per- 



manent ; because the colouring matter 

 would be very soon rubbed off; and would 

 totally disapjjear whenever the cloth was 

 washed, or even exposed to the weather. 

 The colouring inatter then, however per- 

 fect a colour it possesses, is of no value, 

 unless it also adheres so firmly to the cloth 

 that none of the substances usually ap- 

 plied to cloth, in order to clean it, &c. can 

 displace it. Now this can only happen, 

 when there is a strong affinity between 

 the colouring matter and the cloth, and 

 when they are actually combined together 

 in consequence of that affinity. Dying 

 then, is merely a chemical process and 

 consists in combining a certain colouring 

 matter with fibres of cloth. This process 

 can in no instance be performed, unless 

 the dye-stuff is first reduced to its integ- 

 rant particles; for the attraction of aggrega- 

 tion between the particles of dye-stuffs, 

 is too great to be overcome by the affinity 

 between them and the cloth, unless they 

 be brought within much smaller distances 

 than is possible while they both remain 

 in a solid form. It is necessary therefore, 

 previously to dissolve the colouring mat- 

 ter in some liquid or other, which has a 

 weaker affinity for it than the clolh has. 

 When the cloth is dipped into this solu- 

 tion, the colouring matter, reduced by this 

 contrivance to a liquid state is brought 

 within the attracting distance, the cloth 

 therefore acts upon it and from its stronger 

 affinity takes it from the solvent, and fixes 

 upon itself. By this contrivance too, the 

 equlity of the colour, is in some measure 

 secured, as every part of the cloth has an 

 opportunity of attracting to itself the pro- 

 per proportion of colouring particles. The 

 facility with which cloth imbibes a dye 

 depends upon two circumstances, namely, 

 the affinity between the cloth and the dye- 

 stuff, and the affinity between the dye- 

 stuff and its solvent. It is directly as the 

 former and inversely as the latter. 



It is ol importance to preserve a due 

 proportion between these two affinities as 

 upon that proportion much of the accu- 

 racy of dying depends. If the affinity 

 between the colouring matter and the 

 cloth be too great, compared with the af- 

 finity between the colouring matter and 

 the solvent, the cloth will take the dye 

 too rapidly, and it will be scarcely possir 

 bleto prevent its colour from being une- 



