Iron gall inks have been used for over a thousand years. The medieval scribes who produced illuminated manuscripts, the clerks who kept Victorian ledgers, the architects and notaries who signed documents intended to last centuries — all used iron gall ink. The chemistry is essentially unchanged: iron salts and tannic acid from plant galls, combined in water to produce an ink that starts pale and darkens over time as iron compounds react with oxygen, becoming highly resistant to water and alteration.
Modern iron gall inks for fountain pens are significantly safer than historical formulations — less corrosive to pen components, compatible with regular use in modern fountain pens with appropriate cleaning. They remain the best option for waterproof writing in a fountain pen.
How iron gall ink works
When iron gall ink is first applied to paper, it looks relatively pale — often a bright blue-grey or blue-black. Over the following hours and days, the iron compounds react with oxygen in the air and with the paper fibres, gradually darkening and becoming more permanent. Writing that looked bright blue when fresh may read as near-black a week later. This oxidation is also what creates water resistance: the iron compounds bond with the paper fibres in a way that dye-based inks don't, making the writing much harder to remove or smear when wet.
Safe use in fountain pens
Modern iron gall inks are labelled as safe for fountain pens — and they are, with appropriate care. Two rules apply:
Clean regularly. Iron gall ink should not be left in a fountain pen for extended periods without use. Clean every four weeks minimum, and clean thoroughly before putting the pen away. Iron gall residue can corrode some metal components if left for months.
Don't mix with other inks. Iron gall inks should always be used in a thoroughly cleaned pen — never layered over other inks without cleaning first. Chemical reactions between iron gall and some dye inks can produce sediment that clogs the feed.
Beyond these two rules, iron gall inks are no more demanding than standard dye inks for everyday use.
Diamine Registrar's Blue-Black
The most widely available and most used iron gall ink in the UK. Writes as a vivid, slightly cool blue and darkens to a professional near-black as it oxidises — eventually reading as a very dark blue-black. Highly water resistant once cured. Named for its traditional use in official registers and documents.
The most practical starting point for anyone new to iron gall inks. Reliable, well-behaved, and produces a result that is clearly an iron gall ink (the colour development is visible and satisfying).
Platinum Classic series
Platinum's Classic range is a family of modern iron gall inks in multiple colours beyond the traditional blue-black. The range includes Forest Black (starts as a dark green and darkens), Sepia Black, Lavender Black, Cassis Black, Khaki Black, and others — all following the same iron gall chemistry of appearing in one colour when fresh and darkening over time.
This makes the Classic range uniquely interesting: you can have the waterproofing properties of iron gall ink in colours that wouldn't be associated with permanent document inks historically. Forest Black particularly is remarkable — a green that darkens to near-black, producing writing with a subtle green tint where the oxidation is less complete.
Rohrer & Klingner Salix and Scabiosa
Two well-regarded German iron gall inks. Salix (a dark blue, named for willow) and Scabiosa (a purple-grey, named for the scabious flower) are both good performers with strong water resistance. Slightly different character from the Diamine and Platinum options — a cooler, more European aesthetic that suits formal correspondence particularly well.
Choosing an iron gall ink
For most purposes: start with Diamine Registrar's Blue-Black. It's the most accessible, most documented, and most consistent iron gall ink available in the UK. Once you're comfortable with the format — the colour development, the cleaning requirements — explore the Platinum Classic range for the most interesting colour options in iron gall chemistry.
Browse iron gall fountain pen inks at The Journal Shop.
Where to start: browse our fountain pen inks and fountain pens at The Journal Shop.
