Further Investigations of Colorant Database Development for Two-Constant Kubelka- Munk Theory for Artist Acrylic and Oil Paints

It is a common practice to prepare tint ladders of each colorant consisting of five or more concentrations in order to develop a colorant database for instrumental-based color matching, characterization of optical properties of a coloration system, and pigment mapping. For two-constant Kubelka-Munk theory, the unit absorption and scattering coefficients for each colorant can be solved by the linear-least-squares method using all the samples in the tint ladder. The objective of this research was to find the minimum number of samples in order to characterize each colorant. For the purpose of pigment identification, a pure pigment (masstone) and a mixture sample of unknown concentration with white paint were sufficient to describe each pigment qualitatively. On the other hand, pigment mapping, which resolves not only colorant constituents but also their concentrations, required a masstone and a mixture sample of known concentration, preferably 40% to 60% with white paint, to quantitatively characterize each colorant. For either case, only two samples were needed, which greatly simplified the process to develop a colorant database. This was tested using artist acrylic and oil paints.