Abstract: An ink composition for writing instruments having a porous writing point, which will write satisfactorily on relatively smooth, hard surfaces (e.g. solid plastic surfaces) and which can easily be erased from said smooth, hard surfaces by merely wiping with a dry cloth or paper tissue. The ink composition contains, as essential ingredients, water, a water soluble dye, a silicone surfactant, and a release agent in which the water soluble dye is insoluble. The ink composition may also contain a wax to prevent dusting. An erasing system including a marking board having a smooth, hard, non-porous surface of plastic and a porous point pen having an ink therein which will deposit uniform, legible traces, markings or lines on said plastic surface and which can be removed therefrom with a dry cloth or paper tissue.