What happens when you point an X-ray gun at a 600-year-old document?
That’s what we have just explored at the National Archives of Finland. Among parchment filled with centuries-old handwriting, we carefully measured medieval charters to uncover something invisible to the naked eye: the chemistry and composition of ink.
The star of the show? Iron gall ink.
For hundreds of years, it was the ink of choice in Europe. Made by mixing oak galls, iron salts, and sometimes wine or vinegar, the result was a deep black-brown ink. It was well used by scribes, though it came with a dark side: over time, the same chemistry that made it durable could also slowly eat through the parchment.
Portable X-ray fluorescence (pXRF) is a non-destructive scientific method that helps us find out what elements are present in a material, without taking any samples. With pXRF, we can spot the elemental fingerprints of this ink, especially iron (Fe). These traces help us see where and how inks were prepared, traded, and used. Together, they form the map of medieval craftsmanship: What once flowed from a quill in a candlelit scriptorium now gives us scientific data, connecting the human and material stories of the past.
Big thanks to Eero Ehanti for enabling the collaboration with the Finnish Heritage Agency, and to Jukkapekka Etäsalo and Henni Reijonen for their skilled help during the measurements!