For a long time I’ve been curious about iron gall ink. It’s a term that gets used a lot by archivists, which is unsurprising when it’s the name for the favoured ink used in Europe from the middle ages into the twentieth century, with its use spreading around the globe. It’s the ink used on the oldest document in the University Archives that mentions the University as a corporate entity (dated 1214) and it’s likely to be the same type of ink used in some of the records of the University in the 1800s.
As well as its rich colour and permanent quality (it is remarkably resistant to water), the ink is also known for a less positive aspect – over time it may “eat” through the paper. I vividly recall seeing a photograph of piece of sheet music which had been written using iron gall ink. After 200 years, the corrosion of ink had left the sheet looking like a pianola roll.
I decided, in order to appreciate the ink a little better, the best thing to do was to make some, using an original recipe, and reading secondary sources to understand the process. The recipe I settled on (as guided by this video) was that of Ugo da Carpi, Thesauro de Scrittori (Rome, 1535), reproduced in Renaissance Secrets: Recipes and Formulas (Wheeler, V&A Publishing, 2009). The recipe reads
“Take an ounce of gallnuts crushed into little pieces. Then put into a linen cloth. Tie it up, but not too tightly. Leave to soak for at least six days in 12 ounces of rainwater. Next boil until it reduces down to 8 ounces. Strain and add a quarter ounce of German vitriol, ground to a fine powder and half an ounce of gum arabic, steeped in vinegar[…] And you will make a wondrously good ink”
Gallnuts can be found on a variety of vegetation, but are perhaps best known on oak trees, where they are often called oak galls or oak apples. They are formed after certain types of insect (often a gall wasp) lay their eggs on a tree. When the eggs hatch as larvae, the larvae secrete chemicals which irritate the tree, causing it to produce gall tissue. The gall tissue acts as both a food source for the larvae, and a protective structure in which the larvae can pupate into a wasp. Last year, I asked my family and friends to gather any galls they might see and I noticed they brought back two types – one smooth and round, and the other rather wrinkly.
A Google search reveals that the wrinkly type are caused by the oak knopper gall wasp, and I think the smoother kind are from the oak apple gall wasp (although they are rather small for this type). I wasn’t sure if I could use the wrinkly type in making ink. Most of the YouTube videos showing ink making seem to show the smoother kind, and so I discounted the wrinkled type. Initially, the galls gathered were rather green, and so I left them to ripen to the brown colour that seemed in popular use. By January, they were ready. Unfortunately, I did not have the ounce required by the recipe and so (keen to get going) I bought some galls online. This provided yet another kind of gall. Given their size and their spiky surface, I believe that these may be Aleppo galls. I also purchased Iron II Sulphate (the modern name for German vitriol, or Copperas) and some Gum Arabic.
With a sudden wealth of galls, I decided to make two batches of ink – one with primarily “home gathered” galls, and one solely made with the purchased galls.
The first stage of the recipe is to crush and steep the galls in rainwater. Typically, early January was one of the very few periods in the UK with absolutely no rain. Feeling frustrated that I had nearly all the of the ingredients I needed, I turned to Assistant Keeper Alice Millea, who had previously mentioned she had water butts in her garden. Alice kindly agreed to the (admittedly odd) request, and brought in a flask of rainwater.
I measured out two jars of 12 ounces of rain water. Next, I set to crush the two sets of galls, using a pestle and mortar, starting with the batch primarily gathered nearby. However, the pestle and mortar did not work well on this batch, as the galls were rather spongy and could best be torn apart by hand.
In contrast to this, the purchased galls were extremely hard and took quite some work with the pestle and mortar to reduce to a reasonable size. From da Carpi’s use of the word “crushed” in the recipe, I would presume he was most used to working with Aleppo galls, given their hardness.
I placed the ripped and crushed galls on squares of muslin (usually used for my jam making!) and tied them into what I can best describe as giant tea-bags. I carefully lowered them into the jars of rainwater, and left them to steep for six days.
The purpose of this process is to leech out gallotannic acid from the galls, which will react when further ingredients are added at a later stage of the recipe.
After six days the liquid had turned a strong tea-like colour, and there was a small amount of growth on top of the liquid.
Thus, I strained the liquids again, after removing the galls, through another square of muslin, before boiling each of the liquids until they were reduced to 8 ounces in weight. Whilst the liquid was boiling, I prepared the other ingredients. I was especially struck by the beautiful pale green colour of the Iron II Sulphate.
I wasn’t sure what the recipe meant by “steeping” the Gum Arabic in vinegar, so I decided to make a reasonably thick paste. I used red wine vinegar, as I thought this might have been the most readily available vinegar accessible for most of the period in which the ink was in use.
Eventually the liquid was sufficiently reduced, and an even deeper brown colour. I decanted this into clean jars.
The first ingredient to add was the Iron II Sulphate. The reaction was immediate and impressive.
The change from transparent brown to dusky black was striking. What’s happening is a chemical reaction. When the tannin (from the gallotannic acid) interacts with the iron sulphate, it forms a “ferrous tannate complex”, essentially a dusky-coloured pigment.
The addition of Gum Arabic serves a number of practical purposes. It acts as a suspension agent for the pigment particles present in the liquid, keeping them distributed throughout the ink. It controls the thickness and flow of the ink, ensuring it is the right consistency for writing. It also controls the absorption of the ink into the writing surface, keeping it “on the top” for a little longer, before allowing the ink to be absorbed into the paper or parchment, making for sharper, cleaner writing marks.
Vinegar isn’t present in all iron gall ink recipes, but it is credited with slowing down the settling of pigment particles to the bottom of the ink, and with inhibiting mould growth during storage.
I could hardly wait to try out the ink (having a new dip-pen ready and waiting) but I restrained myself and waited the suggested 24 hours. Both inks when opened smelled of vinegar, but not overwhelmingly so. It’s a very thin liquid, easy to overload the pen. One noticeable difference between the two inks is that the “home grown” gall ink was black the moment it hit the page, but this could have been partly due to an overabundance of ink on the pen.
In contrast to this, the bought gall ink was rather pale when first applied. However, this colour darkened within a few minutes to jet black. The reason for this change in colour is that the iron ions in the mixture oxidise with the air, producing (from the ferrous tannate complex) a ferric tannate pigment with a darker colour, and thus a darker ink.
Furthermore, whilst the ferrous tannate complex is water soluble, the ferric tannate pigment is not, making the ink water resistant.
One final piece of curiosity was, unfortunately, not to be satisfied. I have often wondered what made different varieties of the same ink act so differently. Why do some versions of the ink “eat through” parchments, whilst others affect no damage to the surface? An obvious component is the acidity of the ink, and given that the galls are a variable source of gallotannic acid, I wondered whether different batches of galls would produce different amounts of acid. The Bodleian Conservation department very kindly provided me with some pH testing strips. Unfortunately, the ink simply turned them black, preventing any readings from being taken!
A small warning to those who intend to experiment for themselves – do remember to tighten the lid before shaking the ink…
Sources, Further Reading and Watching
Wheeler, Jo, and Katy Temple. Renaissance Secrets: Recipes and Formulas. London: V&A, 2009.
https://en.wikipedia.org/wiki/Iron_gall_ink
Thank you for the suggestion!
Could you just measure the pH using a meter?