A client of mine has installed an ion exchange water purifier to de-harden her tap water. After that, however, she noticed that it has negatively affected her watercolor painting. From what she describes, it seems that the pigments have flocculated. I have a theory of what may have caused it, but I wish to run it by the community here/inquire about any alternative theories.
The ion exchange filter captures Ca2+ and Mg2+ and exchanges them for Na+, while carbonate and sulfate ions slip through. The original hard water had in other words the presence of partially dissociated CaCO3/CaSO4/MgCO3/MgSO4 species. The ion exchange of Ca2+ and Mg2+ for Na+, however, leaves a different ionic profile consisting of Na+, carbonate, and sulfate ions. This resembles the ions present when N2SO4/N2CO3 dissociate completely, forming a strong electrolyte solution.
If that is correct and we assume that the new water behaves like a strong electrolyte solution compared to regular hard water, then the electrical double layer surrounding the pigment particles ought to be affected --> electrostatic repulsion decreases --> pigments flocculate. However, the DVLO theory states that it is the valency of the electrolytes present and their concentrations that affect particle dispersion, not whether the solution is considered a strong or weak electrolyte. Therefore I am not entirely sure whether I am on the right track.
Am I on the right track thinking that it is the change in electrostatic repulsion that causes my client's watercolor problems or is there something else I am missing? If it is the electrostatic repulsion that is affected, then how exactly?