The invention disclosed herein is a carbon-based surface treatment and method of application that, when applied and heat-treated properly, confers excellent sodium wetting properties to a substrate. Examples of substrates include metals, glass, or ceramics, with a focus on sodium-ion conducting ceramics such as the sodium beta-alumina solid electrolyte (BASE) that is commonly used for various types of sodium batteries. Other examples could include other sodium ion conductors such as NaSICON. The surface treatment is in the form of a slurry or suspension of carbon-black, dispersed in a solvent, which may include an organic solvent, water, or a mixture of these. Additionally, co-solvents may be appropriate to optimize various properties of the suspension, such as dispersion of carbon-black, rheological properties, evaporation rate, wetting on the substrate of choice, etc. Further, a surfactant or detergent may also be added, with the goal of maintaining dispersion of the carbon-black and wetting on the substrate of choice. Finally, a binder may be added, which is intended to modify rheology, facilitate stiction of the wetting layer to the substrate after application, and provide mechanical adhesion and strength to the carbon-black layer.