Fig. 9. Contour plots of print through value over surface tension γ and viscosity η. Each plot illustrates one substrate from Table 2. The contour lines represent combinations of γ and η resulting in same print through. The horizontal lines show a strong influence of viscosity for the unsized papers. The sized sheets are influenced by both parameters, viscosity and surface tension (bottom), indicated by the changing slopes of the contour lines into a less horizontal direction.