Nicholas C. Lewis posted a decent open source inkjet[0] on Thingiverse. He had a Kickstarter for his inkjet cartridge controller[1], which I later used for something silly[2].

0: http://www.thingiverse.com/thing:8542

1: http://nicholasclewis.com/projects/inkshield/

2: http://eclecti.cc/hardware/semi-automatic-paintbrush