Continuous inkjet
An industrial inkjet that sprays an unbroken stream of drops and steers them electrically — most are recycled.
Here droplets form constantly, tens of thousands a second, as a jet of ink breaks up under a pressure wave (Rayleigh instability). Each drop is selectively charged and then steered through an electric field: those meant to print land on the product, the rest are caught in a gutter and pumped back. Because the jet never stops, the nozzle can't dry out, and the throw distance can be large — which is why CIJ marks best-before dates on bottles, cables and packaging at full line speed. The technology traces to Richard Sweet's work at Stanford in the 1960s and was commercialised by Videojet among others.