Potential methods for predicting the visual impression of the opacity of translucent white ink were evaluated. An experiment was conducted to collect visual data for white ink coatings on three different substrates: white paper, clear film and kraft paper. The contrast ratio metric used for paint and varnish coatings, together with other proposed methods, were tested as correlates for the visual data. The contrast ratio, based on the difference in reflectance between ink printed on the substrate and over a black ground, performed most consistently across the three substrates, while other correlates, such as relative lightness or colour difference, performed better for ink on certain substrates. The results also indicate that a method that does not use black ground under the coating may provide better results when the substrate differs significantly in appearance from the ink.
Helene Midtfjord, Phil Green, Peter Nussbaum, "A Model of Visual Opacity for Translucent Colorants" in Proc. IS&T Int’l. Symp. on Electronic Imaging: Material Appearance, 2018, pp 209-1 - 209-6, https://doi.org/10.2352/ISSN.2470-1173.2018.8.MAAP-210