Farhad Ameri

This paper presents an experimental investigation into the estimation of specular gloss from the colorimetric data. The 28 samples were selected from the Natural Color System (NCS) gloss scale, which had different combinations of lightness and gloss levels. The samples’ spectral reflectance and colorimetric data Y and L* were measured by a d:8° geometry reflectance spectrophotometer in both SCE (Specular Component Excluded) and SCI (Specular Component Included) modes. Additionally, the specular gloss of the samples at three common angles 20^◦, 60^◦, and 85^◦ was measured using a gloss meter. The correlation and relationship between DY_SCI-SCE and DL*_SCI-SCE and the specular gloss values measured for the samples at different angles were evaluated and analyzed with linear and second-polynomial regression functions. The results were validated with a different set of data acquired from 32 random solid-coated samples. The results showed the best fitting was achieved at 60^◦ of gloss measurement with a second-polynomial function. As the specular gloss of DY decreased, like in a matt sample, the estimation error of specular gloss increased with a large error of over 10%.

K/S and reflectance graphs are essential tools in characterizing the dyeing behavior. In textile coloration, estimating the dye concentration is poor using the Kubelka-Munk model due to its low scalability and deviation of the reflectance function from linearity after low dye concentrations, particularly in the wavelengths where the gradient of K/S against dye concentration is noticeable. This paper focused on extending the validity of the Kubelka-Munk function, which originates from the linearity of reflectance function against higher dye concentration. A data set of dyed polyester specimens with three disperse dyes in a dye concentration range was prepared. At the present work, K/S was analyzed by describing the scalability property, and the suitable wavelengths in the visible spectrum where K/S benefits from minor deviation from linearity were also discussed. It was observed that the K/S function is not always scalable and deviates in λ _max after a specific dye concentration for K/S > 17. Accordingly, the wavelengths other than λ _max were found that could be as important as λ _max . For the K/S values > 25, no practical region was achieved.

Measuring gloss, visually or instrumentally, has been a challenge in many manufacturing and service industries. However, there exists no standardized method for visual evaluation of equidistance specular gloss. This study aimed to design and prepare a psychometric visually equispaced specular gloss scale for the visual measurement of gloss or any other geometric appearance attribute. To this end, a series of lithographically printed black papers, with different levels of gloss from low to high, were prepared to constitute a visually uniform specular gloss scale. Fourteen observers visually quantified the scale in a unidirectional illumination at three different geometries. Analyzing the results shows that the 60° geometry can quantify the equivalent specular gloss efficiently. A uniform specular gloss scale was prepared by assessing the prepared scale visually under the unidirectional illumination at the 60° geometry. Such a visually uniform specular gloss scale could be employed to develop a standard visual evaluation method of specular gloss in all related industries.