example in the topmost curve the printer prints 0 78 of the drops emitted by the nozzles in other words 99 22 of the ink is recirculated the bottommost curve represents a print drop usage rate of 3 1 where 96 9 of the ink is recirculated the latter printing job would contain large black areas the typical text or printed page would be on the 1 55 print drop usage curve the graph in fig2 makes it very clear that as the print drop usage rate goes up evaporation of the ink is less of a problem this is because the ink is being used at a sufficientially rapid rate that evaporation has a small effect on the quantity of ink even though the evaporation rate may be high as the print drop usage rate goes down the evaporation rate becomes more critical the 25 more concentrated line indicated on the vertical axis is approximately the point where the ink becomes unusable beyond this point the ink nonvolatiles may precipitate and create problems in the ink system thus the graph in fig2 makes it apparent that to operate at various print drop usage rates and to maintain ink concentration at acceptable levels it is necessary to have low evaporation ink recirculation apparatus the apparatus of the present invention has operated at an evaporation rate of 0 12 in an ambient environment of 73 degrees f 21 degrees c approximately 40 relative humidity with vacuum of 4 34 10 cm of water pulled on the ink reservoir and 76 degrees f 23 degrees c.