After the printing is done, the printhead goes in the capping station, where it is is sealed with a rubber cap. The cap is nearly air-tight and the evaporation rate is drastically reduced there, however, it is not completely stopped, and some water loss continues. In addition to this, if the inks are pigment-based, the pigment particles gradually settle under the action of gravity, as it sits in the cap. If settling is very strong, a sludge is formed in the area by the nozzles, and, unless this sludge is removed, the printhead will have a difficulty to print again.
Every time the customer comes from an extended break, such as vacation break, he or she expects the printer to work normally and to start printing again. In many cases , it is difficult to accomplish! Some pigmented inks, for example carbon black or titania based (black or white) are in particular difficult. On the printer side, there are many algorithms that help the printhead to remain healthy as it sits in the cap. Those include out-of-cap servicing, which is extensive spitting and wiping of the printhead after a long break. On top of that, the printers often wake up at night and do some servicing to the nozzles. An inkjet printer never truly sleeps!