and
S. G.
At the p r e s e n t time, subjective methods of d e t e r m i n i n g the b a s i c c h a r a c t e r i s t i c s of c o l o r such as its b r i g h t n e s s , c o l o r tone, and purity a r e still widely employed in the textile industry. These methods depend upon the o b s e r v e r and the conditions of illumination and r e n d e r disputable c o l o r values in many c a s e s . In [ 1] an obj ective speetrophotometric technique was used. The basic idea of the method is to d e t e r m i n e the a b o v e - i n d i cated color c h a r a c t e r i s t i c s of fabrics f r o m their diffuse reflection s p e c t r a . The c o l o r c h a r a c t e r i s t i c s obtained with this method a r e independent of the illuminating s o u r c e and the r e c e i v e r and depend only upon the p r o p e r t i e s of the dyed fabric and the dye. The p r e s e n t work c o n s i d e r s the c o l o r c h a r a c t e r i s t i c s of dyed fabrics depending upon the p h y s i o c o c h e m i c a l nature of t h e i r fibers, the s t r u c t u r e f a c t o r s , and the dye. Investigations have been made on synthetic v i s c o s e f a b r i c s , a r t i c l e n u m b e r s 32494, 32395, and 72110, cotton fabrics with article n u m b e r s 328, 1465, and 520, f a b r i c s made f r o m synthetic fibers (Capron) with a r t i c l e numbers 52001 and 230910, and natural silk with a r t i c l e n u m b e r 11022. All f a b r i c s w e r e dyed by d i r e c t dyes: fast blue KU, fast g r e e n Zh, and fast s c a r l e t and orange. The synthetic f a b r i c s and the natural silk were also colored by acid dyes: fast orange, s c a r l e t , g r e e n Zh, blue 2K, and yellow. The dye solutions were p r e p a r e d according to All-Union State Standard (GOST) 7925-56 for each dye at the concentrations C = 0.3, 0.6, 1.0, 1.5, and 2.0~, r e f e r r e d to the weight of the sample. The absolute values of the s p e c t r a l coefficients of diffuse reflection of the fabric s a m p l e s of " i n f i n i t e " thickness (number of fabric l a y e r s for which the t r a n s m i s s i o n p r a c t i c a l l y no longer exists) w e r e m e a s u r e d with the s p e c t r o p h o t o m e t r i e setup and the technique d e s c r i b e d in [2, 3]. The brightness, the c o l o r tone, and the purity of c o l o r were d e t e r m i n e d as in [ 1]. F i g u r e l a - b and Table 1 list the c o l o r c h a r a c t e r i s t i c s of the dyed v i s c o s e f a b r i c s having the s a m e c h e m i c a l n a t u r e of the fibers but different weaving s t r u c t u r e s . Obviously, the absolute values of the c o l o r p a r a m e t e r s differ c o n s i d e r a b l y for all concentrations and depend upon the type of the dye. In the c a s e of fabrics dyed with d a r k e r blue dye, the differences in the brightness and purity values of the c o l o r a r e slightly s m a l l e r than in the c a s e of the b r i g h t e r orange dye. Moreover, when the concentration of the dye i n c r e a s e s , the b r i g h t n e s s of the fabrics d e c r e a s e s slowly in all c a s e s but the p u r i t y of c o l o r i n c r e a s e s . T h e s e relationships can be explained with the information on the s p e c t r o s c o p i c p a r a m e t e r s of these v i s c o s e f a b r i c s : a b s o r p t i o n coefficient ~ and s c a t t e r i n g coefficient ~ of a volume unit of the m a t e r i a l [4, 5]. Since, a c c o r d i n g to [4], the values ~ = 600, 450, and 250 c m -1 hold for the undyed fabrics article n u m b e r s 32494, 32395, and 72110, r e s p e c t i v e l y , the b r i g h t n e s s of c o l o r i n c r e a s e s with i n c r e a s i n g s c a t t e r i n g of the fabric, whereas the p u r i t y of the c o l o r d e c r e a s e s . With i n c r e a s i n g dye c o n c e n t r a tion and a slowly changing a, ~ i n c r e a s e s , which, in turn, reduces the b r i g h t n e s s and i n c r e a s e s the purity of color. Let us note that for the d a r k e r blue dye, the values of the a b s o r p t i o n coefficient ~ a r e g r e a t e r than for orange at the s a m e concentrations. This implies that s c a t t e r i n g in the s u p e r f i c i a l fabric l a y e r is of g r e a t e r importance, whereas the s c a t t e r i n g f r o m the deeper l a y e r s is important in the second case. Thus, in the c a s e of the orange dye, the differences in the weaving s t r u c t u r e of the f a b r i c s examined m a n i f e s t t h e m s e l v e s m o r e c l e a r l y in the changes of b r i g h t n e s s and purity of color. The data of Table 1 indicate that the wavelengths ( k e f f ) f a b r , which d e t e r m i n e the c o l o r tone of the fabric, a r e shifted in all c a s e s relative to ( keff)dye = 380 nm, which l a t t e r value d e t e r m i n e s the c o l o r tone of the dye in the solution. The shift takes place toward longer wavelengths and is g r e a t e r the higher the s c a t t e r ing capability of the fabric (higher a) [4]. However, when the dye concentration i n c r e a s e s , the differences b e tween ( k e f f ) f a b r and (keff)dy e d e c r e a s e and p r a c t i c a l l y d i s a p p e a r in the limit at C = 2.0%. F i g u r e l c - d shows the concentration dependences of the b r i g h t n e s s and the purity of c o l o r for three fabr i c s with the s a m e weaving s t r u c t u r e (plain weave). In this c a s e substantial differences in the absolute values T r a n s l a t e d f r o m Zhurnal Prikladnoi Spektroskopii, Vol. 35, No. 3, pp. 502-507, September, 1981. O r i g i nal a r t i c l e submitted October 28, 1980.