They did not use ink. It is actually a stylus used to write on wax tablets (https://en.wikipedia.org/wiki/Wax_tablet https://en.wikipedia.org/wiki/Wax_tablet).

They did not use ink. It is actually a stylus used to write on wax tablets (https://en.wikipedia.org/wiki/Wax_tablet https://en.wikipedia.org/wiki/Wax_tablet). Later in the article it says ... Other finds included more than 400 waxed writing tablets, which offer insights into the first decades of Roman rule in Britain.