US Patent 7101104 Free ink system

A free ink marking instrument for dispensing an ink, including a housing, a reservoir for storing ink within the housing, a feed tube to convey ink communicating with the reservoir, a tip disposed within the feed tube for conveying ink to a substrate at a marking end of the tip, a porous buffer disposed within the housing adjacent the feed tube and configured for storing ink during periods of a decreasing pressure differential between the reservoir and the atmosphere, and bubble separation area in the form of either a hole in the feed tube or a hole or passage formed between the feed tube and the tip, is disclosed.