Epson TM-C3400 User Manual page 25

Note:
When the ink cartridge is installed for the first time, the printer uses ink to
prepare for printing (ink charging).
Cartridge yields vary based on such factors as type of item printed, print
settings, paper type, frequency of use, and temperature.
To insure print quality, some ink remains in the cartridge after the Ink LED
comes on.
The ink cartridge contains 3 colors of ink. Even when one particular color is
specified, all 3 colors of ink are used for printing and for keeping the print
head in good condition. When the ink level of even one color comes to the
lowest limit, the printer stops printing.
TM-C3400 User's Manual 23