Abstract: A printing ribbon spool which is leak-proof even at less than atmospheric pressure and which has an indefinite shelf life. The spool utilizes a central hub as an ink reservoir and has an ink-impervious member forming a portion of the reservoir isolating the ink from an ink-delivery pad before actuation. The central tubular portions of the spool are interlocked in such a manner that the spool is leak-proof. The ink-impervious member can be pierced by a pin to actuate the spool. Air compensation grooves are utilized to maintain air flow which results in uniform distribution of the ink throughout the pad. The edge of the ribbon contacts the pad and becomes saturated by capillary action to provide uniform and consistent printing for millions of characters.