From Nature’s blog “The Great Beyond” (and other places:
Phil Wilby, a researcher at the British Geological Survey who is behind the discovery of the fossil and the subsequent drawing, ground the solidified, black ink from a fossil of an ancient squid like animal (Belemnotheutis antiquus) and then mixed it with ammonia to create a paint then used to draw a picture of the animal. This might suggest that the ancient ink has similar properties to modern ink, something that awaits confirmation from Yale University in America where it was sent for an in-depth chemical analysis, after which the results will be published.
Wilby told Nature that “fossil cephalopod ink has been found in even older specimens (more than 300 million years old) and, counter intuitively, appears to be amongst the most frequently fossilised soft tissues.”
The fossil was discovered in the long lost Victorian excavation site in Trowbridge, UK, which was renowned for the abundance of soft-tissue fossils. After re-discovering the site, Wilby and his team reported their preliminary findings from a trial excavation in Geology Today last year.