Crystalline ink is an invisible ink that has a special property of its structure being easily changed by magic. If you changed the structure of the ink, the color of the ink would also changed. The ink can turn into any kind of color. After this ink was discovered, it began a revolution in art and literature. The spell to change the ink's color was one of the first spells that was taught in school. The spells is different for argel and elibu because argel uses augmentation magic and elibu uses transmutation magic.