Method of making and improved compositions for an initially erasable ink for a ball point writing instrument

The method of making an ink composition for ball point pen writing instrument, which composition when applied by the pen as a trace on a porous substrate such as paper will exhibit the characteristic of initial erasability by ordinary pencil eraser but developing indelibility with time, which comprises the steps of:

• forming an elastomer solution without pre-mastication of the elastomer and in the absence of milling by selecting a polar elastomer and contacting it, with stirring, with a volatile solvent for the polar elastomer until the polar elastomer swells in the volatile solvent and forms a smooth, homogeneous single phase, the solvent having a boiling point at atmospheric pressure of less than 180.degree. C.;
• and
• adding to said single phase, with mixing, a trace intensity colorant amount of pigment having a particle size of less than about 5 microns, a writing smoothness and viscosity adjusting amount of an essentially non-volatile solvent component having a boiling point at atmospheric pressure of greater than 300.degree. C., and a viscosity adjusting and indelibility-with-time controlling amount of a low viscosity, essentially non-volatile solvent component having a boiling point at atmospheric pressure which is within the range of 180.degree.-300.degree. C., and continuing such mixing until a smooth, homogeneous final ink composition having the consistency of a relatively loose-structured gel and a viscosity of about 1.5 million cps is attained.