One of the few modern manufacturers that produces iron gall ink, Rohrer & Klinger offers two shades of this historically significant formula: Salix and Scabiosa. Made from oak apples, iron gall ink has been used by the likes of Leonardo da Vinci, Johann Sebastian Bach, and was even used in the drafting of the United States Constitution. Rohrer & Klingner’s modern formula will change color over time due to oxidation, and is not recommended for all pen types due to possible corrosion. Iron gall ink requires regular cleaning and should not sit inside your pen for extended amounts of time, as it is prone to staining and clogging.