Destin Sandlin, host of the YouTube show Smarter Every Day, recently devoted an episode to exploring an interesting topic: the science of tattooing.
The episode, above, explores a few different aspects of tattooing, including the mechanisms that power tattooing machines and how exactly they inject ink into our skin.
Below is a coil tattoo machine. The way it works is surprisingly simple: when the circuit is connected, a pair of solenoid coils (the two large cylinders) create a magnetic field, pulling a bar magnet downward and pushing the needle out. When the bar magnet is pulled down, it then breaks the circuit, causing it to bob back upwards on a spring.
This causes it to bob up and down at a very fast rate, as the circuit is completed, then broken, then completed, then broken. Here it is, slowed down significantly:
Sandlin also got permission to film someone getting tattooed in slow-motion. Below is a tattoo artist working with a shading needle — a group of seven needles that plunge down in unison.
When the needles break the skin, they drive ink into the dermis (the layer of skin just below the surface). Ultimately, that ink is permanent because of a quirk of the human immune system: The body responds to the wound with white blood cells that attempt to engulf and remove intruders, but ink pigment particles are simply too big to be eaten.
For an even better look, Sandlin also filmed it at a glorious, skin-jiggling 3200 frames per second. Enjoy:
Correction: This article originally referred to the tattoo machine's solenoid coils as batteries.