The use of crystallization inhibitors has been proposed as a potential preventive treatment method against damage and is extensively tested for crystallization of single salts. However, in practice salt mixtures are present. Therefore, before using inhibitors in practice there is a strong need to explore their effect on salt mixtures. In this research, we studied the effect of ferrocyanide ions ([Fe(CN)6]4−) on NaCl crystallization in single salt and in salt mixtures of NaCl–KCl and NaCl–LiCl. A series of micro droplet drying experiments were undertaken. Time lapse microscopy of the crystallization was performed along with NMR measurements of hydrogen, sodium and lithium ions. This gives the possibility to visualize the drying of the droplet while simultaneously obtaining information of both NaCl and LiCl concentration in the droplet. For a NaCl solution droplet, in the presence of inhibitor, a significantly higher supersaturation prior to the onset of crystallization and a change in crystal morphology were observed. On the other hand, for salt mixtures, lower supersaturation compared to single salt and dendritic crystal morphology was seen in the presence of inhibitor. In a porous material, such a type of morphology can promote the formation of efflorescence that causes only little structural damage.