Every time the printer loses power for long enough to cause the portion of ink which was being kept above its "freeze point" in the printhead to drop below that temperature, the mass of ink in each reservoir would have contracted in size enough (as a result of the cooling) to permit air to enter the printhead, which would result in print aberrations until the printhead reservoirs had been refilled by the ink-melt assembly above it. As a result, the printhead is then purged using a vacuum pump, causing some ink to be flushed from the printhead's holding tanks into the waste tray to remove the air from the printhead. (Xerox printers have a "waste ink" tray for this purpose. Since all four inks are dumped into a unified "waste ink" tray, it is impossible to reuse the lost ink since the four process colors coalesce to form a single solid mass in the tray, which look much like solidified candle wax drippings, but almost black.) If the printer was in its sleep state, less time without power would be required to necessitate a purge cycle than if the printer was in its ready-to-print state (since the printhead is kept much hotter when ready-to-print).