There are two important principles of veganism that most people don't understand. More food is vegan than is immediately obvious. But more seemingly innocuous products have animals parts in them than the average meat-eater imagines. Case in point: tattoos.
As Tim Donnelly writes at The Atlantic, "The ink and processes at your average shop contain a veritable buffet of animal detritus: charred bones of dead animals in the ink, fat from once-living things in the glycerin that serves as a carrying agent, enzymes taken from caged sheep that go into making the care products."
And you're putting that in your body! Forever! Granted, having bone and fat in your body is pretty much standard procedure, but normally it belongs to YOU, not some random cow.
I'm trying to decide if this new information makes me feel differently about my own tattoo. Maybe? The vegan alternative is not that much more appealing — some vegan ink uses plastic. And although some artists say it doesn't make a difference, vegan ink might have less depth of color than the bone-based variety.