I once theorized that the reason that you can never find a pen when you need one is that they evaporate. If this theory is true then it should be possible to saturate the air with pen vapor so that they no longer evaporate (or, more precisely, they condense at the same rate as they evaporate, so the total number of solid pens remains the same).
In an effort to test my theory, I once emptied the supply cabinet at work and distributed the pens around the office. When I was finished, there was no office or desk that didn't have twenty times as many pens as they could possibly use in a year. It seemed to work for a while, but within a month or so, it was getting hard to find a pen again.
My conclusion is that the vapor pressure of pens is so high that it just isn't practical to try to keep the air saturated.