TONER IS ONE of those everyday products we all take for granted. When the printer runs low you pop a new cartridge in—out of sight, out of mind. Well, we got to wondering what’s actually in that cartridge … so we busted one open. Bad idea! (More on that later.) But we’re all cleaned up now and back with answers.
Turns out toner is mostly powdered plastic—and that’s key to the whole technology. Plastic has two handy properties: You can move it around like magic with static electricity, and then you can melt it onto the paper for crisp, smudge-proof images. This technique of printing with powder instead of ink is called xerography (xeros is Greek for “dry”), and it works the same whether you’re printing or copying. In fact, Gary Starkweather invented the laser printer at Xerox in 1969, in a famous bit of rogue engineering, by modding one of the company’s office copiers. (He had to work in secret after his boss ordered him to drop the idea.)
See, a photocopier has a rotating drum that’s coated with a semiconductor like selenium; that coating converts light into electricity, just like in a solar cell. By bouncing bright light off a hard copy (… or select parts of your anatomy) and onto the drum, it creates a ghostly reflection of the original in static charges for toner to stick to. Starkweather realized you could use the same rig to print digital files by scanning a laser directly on the drum. The only difference is in how the electrostatic image is generated. Read more.