Beyond Colorants: Understanding Dilution Effects on Color Attributes in Transparent Systems

ABSTRACT The objective of this work was to evaluate the chromatic displacement due to successive dilutions of different colorants in transparent liquid systems. The solutions were diluted to cover the entire range of transmittance values, from transmittance approaching zero (close to the black achromatic point) to nearly 100% (white achromatic point). Nine colorants, covering a wide range of hue values, were employed; the transmittance of the solutions was spectrophotometrically measured in the visible range, and the tristimulus values were calculated for illuminant D65. 3D representations in CIE, CIELAB, and CIELUV spaces were performed, along with the corresponding planar projections. Besides the expected lightness increase, as the concentration of a given colorant decreased, saturation (in the CIELUV space) and chroma (in the CIELAB space) increased up to a given value and then decreased. Colorants' dilution led to different trajectories in the chromaticity diagram, causing perceived changes of saturation and hue attributes, slightly correlated with the dominant wavelength shift. These phenomena have been previously observed in opaque systems and in lights and were much less studied in transparent colorant formulations, which are relevant for applications such as glass, films, plastics, or colorant solutions. Some definitions involving concentration as related to change in color attributes, such as the optimal lightness to chroma or saturation ratio and the trajectory change in the chromaticity diagram, are proposed.