Azul Marino ink was a type of ink that the Wizarding Examinations Authority's Magical Regulation 572 required Fifth year students at Hogwarts to use when sitting their O.W.L. exams.
The ink was presumably a deep blue colour (azul marino being the Spanish term for ultramarine).[1]
Appearances

A sign instructing Fifth year students taking their Charms O.W.L. to use only Azul Marino ink
- Harry Potter and the Order of the Phoenix (film) (Mentioned on sign)
Notes and references
- ↑ "Azul marino" on Spanish Wikipedia