The phenomenon of 'wet pick' during printing is well known to paper coating and printing technologists. Recent work has highlighted the reversible effect of water on the tensile strength of coating layers, and has shown that the mineral and vegetable oils commonly used in ink formulations have a similar, if smaller, detrimental effect on strength. In this study, we show that the coating strength decreases as the dielectric constant of the penetrating fluid increases. In the adhesive science literature, a similar correlation has been observed for various types of adhesive joints, and can be explained in terms of ion-pair bonding. We have tested this theory for mineral-based paper coatings containing latex adhesive, and found that it underestimates the loss of strength observed experimentally. In the latex-mineral bond, contributions from other mechanisms such as van der Waals forces are also likely. This knowledge should ultimately allow the design of more effective pigment-binder combinations better able to withstand weakening in the presence of fluids used in printing. (C) Koninklijke Brill NV, Leiden, 2010