METHOD FOR OPERATING A PRINTING DEVICE AND PRINTING DEVICE

In the case of a method for operating a printing device (1), wherein a fluid that is provided for a printing procedure is supplied from a fluid storage container (6) by way of a supply line (14) to a printing head (13) so as to be able to be applied by the printing head (13) onto a surface, the fluid in a purification circuit (2) is conveyed through a purification installation (8), and by way of a contamination-measurement installation (11) a key contamination indicator of a fluid-specimen quantity in the purification circuit (2) is determined such that a printing procedure by way of which the fluid is dispensed from the printing head (13) commences only once the key contamination indicator has undershot a first threshold value. The invention also relates to a printing device (1) having a printing head (13) and having a connector installation (12) for a fluid storage container (6), said connector installation (12) being connected to the printing head (13) by way of a supply line (14), wherein the printing device (1) has a purification circuit (2) that is formed from fluid-line portions (3, 4, 5) and has a purification installation (8) and has a contamination-measurement installation (11) in which the fluid that by way of the fluid retrieval installation has been retrieved form the fluid storage container (6) can be purified, and a key contamination indicator of a fluid-specimen quantity in the purification circuit (6) can be determined before the purified fluid is supplied to the printing head (13).