The ink was derived from a tea leaf that produces a tangy, very bitter taste that is considered a local delicacy, though very few have the leather tongue needed to take more than a few sips. This tea leaf is mashed down, and boiled in a strong spirit, typically a clear neutral ethanol.
The fluid is decanted off and placed in a still, the ethanol is baked off first and recaptured for reuse. The fluid that is left is a base for the ink, and typically mixed with various pigments and minerals for color. Though on a mass produced level it is left in the base color which is dark brown.
After the ink has been stored, the Artificer finally lays their hands on the material. Though new technologies have made the practice easier, it is traditionally applied with steady hands and dull hollow needles. Where the ink only barely penetrates the top surface in contrast to regular tattoos that aim to penetrate deep skin. Making it washable, a simple rinse with soap and water pulls more of the ink out, the body does the rest over the course of a few days as the skin sheds away.
After the rune structure has been applied, the Artificer will do their favorite aspect. Calling it "The Works'', the caster will place their hands over the ink and breathe formless magic into it, no
Domain specifically. Though it should be noted that Arificers are somewhat unique in this regard, whereas most cave specific talents in magic, artificers have many lesser talents and tend to mix them to form a colorless magic so to speak.
The ink acting as the conduit enacts the purpose of the rune, and the intent of the caster. The tattoo will glow softly, then fade beginning its effective use.
This is really cool! It's sad that some workers and soldiers are forced to wear them, but I can understand how they got there.
Ah the inexorable march of the machine, economies at scale rarely see the beauty in something, care only for it's usefulness. I glad you like it!