It's easy to take a medium like ink for granted, until a pen runs dry of course. But ink as an art medium has been around since humans painted cave walls. Early ink mixed soot with water or oil, but in 2500 BCE the Egyptians took it to the next level, grinding down charcoal into a fine carbon powder called 'lamp black' and using gum or glue as a bonding agent. 200 years later ancient Chinese cultures would independently invent inks based on plant dyes.
Ink took new life again in the 6th century CE with the invention of the quill pen, becoming the primary method of recording written language in the Western world. Gutenberg invented an oil-based ink to work with his printing press, and ink continued to evolve all the way to 1988, when Hewlett-Packard's consumer-grade Inkjet printers put the power of the press into the home office.
From the caves to the Inkjet, ink has been used by artists the world over for drafting maps, sketching anatomy, ornate calligraphy and capturing ideas of all kinds. For our money, ink may be the most versatile art medium in history.