ON THE ACTION OF LIGHT UPON DYED COLOURS. 373 



The Action of Light upon Dyed Colours. — Report of Committee^ 

 consisting of Professor T. E. Thorpe {Chairman), Professor J. J. 

 Hummel {Secretary), Dr. W. H. Perkin, Professor W. J. Russell, 

 Captain i^JBNEY, Professor W. Stroud, and Professor R. Meldola. 

 {Drawn up by the Secretary.) 



The object of the Committee appointed to study this matter has been to 

 •determine by experiment the relative fastness to light of the colours dyed 

 ■on textile fabrics with the various natural and artificial colouring matters. 



For this purpose patterns of silk, wool, and cotton have been dyed 

 with equal percentages (2 per cent.) of the various commercial artificial 

 colouring matters. With the natural colouring matters the patterns were 

 dyed to approximately the same depth of colour. 



The patterns were exposed to light at Adel, a country district about 

 -five miles to the north of Leeds, in order to avoid the influence of town 

 smoke, sulphurous acid, &c., the prevailing winds being westerly. The 

 patterns were pinned on deal boards covered with white calico, fixed in a 

 vertical position in glazed wooden cases, so arranged as to permit free 

 circulation of the air and moisture after filtration through cotton wool to 

 exclude dust, &c. 



The exposing cases were set up in the grounds of Jas. A. Hirst, Esq., 

 to whom the best thanks of the Committee are due for his kind permission 

 to do so. 



Each dyed pattern was divided into six pieces, one of which was 

 protected from the action of light, while the others were exposed for 

 different periods of time. The shortest period of exposure, or ' fading 

 period,' was about three weeks (May 24 to June 14, 1892), and a record 

 of the fading power of this period was kept by exposing along with 

 the patterns a special series of ' standards ' dyed with selected colouring 

 matters. These standards were removed from the action of the light along 

 with the first set of dyed patterns at the end of the first ' fading period ' 

 (May 24 to June 14, 1892). The faded standards were then at once 

 replaced by a fresh unexposed series, and these were allowed to fade to 

 the same extent as the first, when, a second period of exposure equal in 

 fading power to the first having thus been marked off, a second set of the 

 dyed patterns were removed from the action of light along with the second 

 series of faded standards. The latter were again renewed as before to 

 mark off the next ' fading period.' The fourth and fifth sets of dyed 

 patterns were submitted to an exposure equivalent to two or three 'fading 

 periods ' in order that the fifth set might have an exposure of one year. 



The above method was adopted in order to be able to expose dyed 

 patterns to an equal amount of fading in different years, irrespective of 

 the time of the year or the conditions of light, moisture, temperature, &c. 

 It was rendered necessary indeed in consequence of the practical impos- 

 sibility of exposing simultaneously a complete set of dyed colours. 



During the year 1892-93 the red dyes on wool and silk have been 

 exposed. For want of sufficient exposing space, however, the Congo 

 colours and some others, as well as the reds dyed on cotton, had to 

 be omitted. During 1893-94 the orange and yellow dyes are being 

 exposed, and the remaining colours will be exposed in subsequent years 



