Solid ink printing was invented by Tektronix first and later by Xerox after they purchased the company. The technology is cutting edge as far as printing goes and avoids normal printer ink or toner cartridges, instead utilizing literally globs of solid ink in the colors that are required. These ink packets are waxy, nontoxic, and you can even hold them in your hand. No cartridges to throw away afterwards.
The mechanism is similar to offset printing, and the solid ink is heated and the melted portion introduced into the print head where it is applied to the paper and cools. Solid ink, because the process is similar and the waxy material more versatile, can actually be used on a variety of papers making it perfect for publishing or comic book applications. And the chemical composition of the ink also makes it possible for the colors contained in the ink to appear much brighter and more vibrant than other methods of printing.
Of course, as with everything there are downsides. The cost of the printers is one, as is the scarcity of third party supplies used to print more cheaply. The printers also, while generating very little waste normally, run through a lot of unused toner if they constantly lose power, making them only feasible for environments with regular printing requirements. Also solid ink printing requires a long warm up time, the printers need several minutes before they are ready to print the first page.
And be careful if you print too much onto a single page as more there is applied to the page the easier it is to rub the ink off.