The colorimetric measurement of mélange woollen yarns: a new optical tool

One of the most critical phases of the production of woollen yarns for knitting and weaving is the comparison between the colour of the finished product and the colour desired by a customer or provided by a catalogue. Accordingly the companies that produce yarns perform a colorimetric control of their products by evaluating the colorimetric distance between the final product, obtained by mixing the coloured raw material, and the desired one. This colorimetric control is mainly performed using a calibrated reflectance spectrophotometer thus allowing an accurate measurement of the spectrum of a woollen yarn. This is performed only in the case of uniform colour. Being the area of the spectrophotometer acquisition sensor very small (20 mm2) when a woollen yarn is composed by two or more colours (i.e. is a mélange woollen yarn), the spectrophotometer is not able to discriminate all the colours reliably. The objective of the present work, developed by the Dipartimento di Meccanica e Tecnologie Industriali of the University of Florence in collaboration with the company Newmill S.p.A., is to develop an optical system (tool) able to perform an accurate colorimetric measurement of melànge woollen yarns on the basis of the combination of flat scanner acquisition and colorimetric techniques.