2ml sample of Private Reserve InfinityBrown fountain pen ink, in a labeled plastic vial. The Private Reserve Infinity Ink collection uses the E.C.O. (Extended Cap Off) technology, a new advanced ink formula which allows a fountain pen user to leave their pen uncapped for a longer period of time without drying out. Your exact results will vary based on your specific pen, environment, etc, but our testing was pretty consistent to be able to leave a fountain pen uncapped for an hour and to have it start writing back up without issue.