INGREDIENTS
Galls, iron, water, gum
The most common recipes used oak galls, iron sulfate, water and gum arabic. Tannins from the galls react with the iron to make a dark ink.
How it was madeStart
WHAT THE CONSERVATORS SAY
The ink
that bites.
Much of the old handwriting in archives was written in iron gall ink.
It was made from oak galls and iron salts, and it was prized because it would not wash away. The same chemistry that fixes it to the page also releases acid, which is why conservators around the world still study it.
BLUE-BLACKand burnt in
Check a pageKeep in mind
- Galls plus iron
- Darkens as it dries
- Acid over time
- A permanent ink with a price
THE SHORT ANSWER
Permanent by design,
corrosive by nature.
Four ingredients, one reaction.
It explains both the beauty and the damage.
PERMANENCE
Etched into the page
Unlike carbon ink, which could flake off, iron gall ink etches the writing surface and cannot easily be washed off. That made it the favourite for parchment.
See the numbers
CORROSION
Acid in every line
The reaction also releases sulfuric acid. Over time it browns and weakens paper, and heavily inked letters can crack or fall out.
Check a pageA QUICK PAGE CHECK
How far has
the ink gone?
Conservators describe ink corrosion in stages. Pick what you can see on an old handwritten page to find the stage. The bar shows how advanced the damage is.
Based on conservation guidance from the American Philosophical Society Library. For valuable documents, ask an archive or a trained conservator before handling or treating them.
TWO NUMBERS WORTH KNOWING
Strong acid,
simple protection.
One figure on why the ink harms paper,
one on how archives slow it down.
1–3 pH
Typical pH of iron gall ink
Forming the dark iron-tannin complex releases sulfuric acid, so the ink is always very acidic. Acids shorten the cellulose chains in paper, making it brown and brittle.
ACIDITY · APS LIBRARY
< 60%
Relative humidity to stay under
With no definitive cure yet, the preferred way to prolong originals is a suitable environment, in particular relative humidity under 60%, plus careful handling.
STORAGE · SURREY HISTORY CENTRE
An EU-funded project, InkCor (2002 to 2005), found that the thickness of the ink layer, the density of the paper and the acidity of the writing material were the most important factors in a document's condition.
FOUR HABITS FROM THE ARCHIVES
Gentle hands,
steady air.
Archive advice for iron gall ink documents is simple and cheap. These habits come straight from conservation guidance, not from a treatment kit.
Step 1
Keep it cool and dark
Surrey History Centre repeats the long-standing advice: cool, dark conditions slow the damage.
Step 2
Dry, but not too dry
Aim for relative humidity under 60%. Changes in temperature and humidity help the ink corrode.
Step 3
Handle as little as possible
Corroded ink can crack when the paper moves, so support the sheet and turn it gently.
Step 4
Leave treatment to experts
Washing and deacidifying badly damaged pages are specialist methods used by trained conservators.
FROM GALL TO PAGE
A wasp, a tree
and a jar of vitriol.
Oak galls are the tree's reaction to wasps laying eggs. Soaked in water, wine or beer, they release tannins and gallic acid. Ferrous sulfate, once called green vitriol or copperas, turns them blue-black, and gum arabic helps the ink flow from a quill or a metal nib.
Fresh iron gall ink often goes on pale brown and darkens to a purplish black as it dries. Because people mixed their own, recipes varied, and inks with more iron than the reaction needed were prone to corrosion.
Questions
Questions on the way
How old is iron gall ink?
Sources differ on its start. The American Philosophical Society says it was developed in the 4th century, Surrey History Centre says it was in use before the 7th century, and the Library of Congress calls it the main Western writing ink from the 12th to the 19th centuries.
Why did scribes prefer it to carbon ink?
Carbon inks could flake off with damp and rubbing, especially from parchment. Iron gall ink bonds to the surface chemically and cannot easily be washed away, so it was treated as permanent.
Why does the writing change colour?
When first applied it is often light brown or sepia, then it turns purplish-black as it dries.
Why does it damage paper?
The ink is very acidic, with a pH of 1 to 3, and excess iron speeds up oxidation of the paper. Together they make paper brown, brittle and in the worst cases full of holes.
Can corroded documents be repaired?
Conservators have treatments, including washing in a calcium ammonium phytate solution and deacidification, but research continues and there is no definitive solution. Good storage and gentle handling remain the first line of care.
Destination
Where the facts come from
- Surrey County Council, Surrey History Centre: The development of iron gall ink
- American Philosophical Society Library: The Ins and Outs of Iron Gall Ink (2021)
- Library of Congress Information Bulletin: Solutions for treating iron-gall ink artifacts (2008)
- CORDIS, European Commission: Protecting historical documents from corrosive ink (InkCor project)
- Maryland State Archives: Common conservation problems
Updated