It actually depends. While homemade inks could be made of anything really, including pen ink or blood, professional inks are usually made of metals, surprisingly, though plastics can be used too.
I love playing find the vegan. The name certainly was a clue, but you don't really need "hints" to find one. All you do is insult a plant or say "I like bacon."
"When they try to impress you-- 'I haven't had meat in 5 years.'"