Iron Gall ink is a type of ink used in medieval times for writing manuscripts and is famous for being extremely long lasting. They are made from iron salts and tannic acids from vegetable sources and are corrosive for steel pens.
However, KWZ's specially designed formula of iron gall ink mak it modern fountain pen friendly ink! You can use it with both your fountain ink and your dip pen. The colour darkens over time compared to some common inks which tend to fade over years, making it a great choice for documents. And you can have fun watching it change colour before your eyes!
Please note that while the iron gall component is permanent, the dyes can be washed away so spraying your work with water is not recommended.
Fountain pen users are recommended not to leave your pen unused when it is loaded with iron gall ink.