The use of coated ink jet papers consisting of components typical for conventional printing papers would be advantageous in small scale applications for economical reasons. This study attempted to gain an understanding of the mechanisms affecting the water fastness of ink jet prints on conventionally coated papers. The effect of the polymer system of the coating was of particular interest. This was studied with FTIR and Raman spectroscopy using dye based model inks and kaolin coated pilot papers with known compositions. The data on water fastness were consistent with the hypotheses of the study. The results indicated that the water fastness of the studied ink jet prints was improved when the impermeability of the coating or its ability to fix the colorants with ionic bonds increased. With hydrophilic coatings, the structural properties of the coatings were of minor importance due to the dissolution of the binder. Rather, the ability of the coating to fix the colorants with ionic bonds proved to be critical. With hydrophobic coatings the structural properties of the coatings had more relevance. In this case, water fastness was improved with decreases in the porosity and wettability of the coating.