Astuvansalmi in Ristiina, Finland, is home to the largest collection of rock paintings in the Nordic countries. Around 80 paintings, estimated to be 5,000 years old, have been discovered at the site so far. Thanks to imaging methods that are based on computer science, entirely new images may yet be discovered on the rock face.
- Text Marianne Mustonen
- Photos Raija Törrönen
An ancient elk gazes into the distance from the steep shoreline cliff of Lake Yövesi. The autumn day is sunny, but very windy.
“We’ve been here for three hours and already discovered three new potential images,” Project Coordinator Veikko Miettinen from the School of Computing at the University of Eastern Finland says.
“Today, we’re testing a brand-new imaging technique that didn’t even exist until recently. The idea of our project is to identify different red pigments on the rock and to determine their age and composition. You can distinguish at least three different shades of red just by naked eye.”
The rock surface features not only clear drawings but also patches of red where different paints seem to have been gotten mixed, and which are of particular interest to the researchers.
“Images taken with a hyperspectral camera allow us to isolate different shades of red and to determine, for example, how many different paint mixtures ancient artists may have used. The imaging techniques and the image analysis applications are based on computer science,” Miettinen says.
Nowadays, these pricey cameras are robust enough to withstand demanding field conditions.
Images create a digital twin of rock paintings
The rock face of Astuvansalmi is documented using several imaging techniques. The entire site is first captured with GigaPan panoramic photography, then scanned on foot using a new three-camera rig mounted on a long arm, along with a Matterport 3D scanner.
A flat surface would, of course, be easier to scan than a curved rock, and cameras cannot see beneath moss, either.
“Difficult-to-capture areas are imaged using a highly precise hyperspectral camera and a system camera,” Miettinen explains.
“We would have liked to fly a drone for imaging as well, but it’s too windy today, so we’ll carry out the drone imaging later.”
Images of the rock paintings can be viewed on a tablet screen using various colour channels.
“A software for image analysis was developed for computers already in the 1990s, and now we’re just simply trying to improve it,” Miettinen adds.
All image data is stored on a cloud server at the site. From these data, a digital twin of the Astuvansalmi rock paintings is created, allowing for their detailed examination on a computer screen.
Imaging techniques for rock paintings and other sites have progressed significantly in recent years. Previously, only three colour channels were available. Now, modern hyperspectral cameras, or scanners, offer hundreds of channels, enabling more precise imaging of surface features.
The Matterport 3D scan of Astuvansalmi is carried out by entrepreneur Rami Saarikorpi from 360Finland.
“Using 3D Gaussian Splatting rendering, we can create an accurate three-dimensional model of the site. By combining data from the site, we can pinpoint exactly where the colours are located,” he explains.
Spectral imaging measures the optical reflectance properties of a surface with high precision across the visible and near-infrared wavelength ranges. Capturing a single highly detailed image with a hyperspectral camera can take a long time, up to several minutes.
Raising Lake Saimaa’s water level to its ancient height with game technology
Astuvansalmi with its rock paintings is not the only site being documented. Researchers have previously imaged rock paintings at Värikallio in Hossa and at Saraakallio in Laukaa.
It’s entirely possible that more rock paintings will be discovered at yet undiscovered sites.
“When these rock paintings were made, water levels were significantly higher than they are now. Our ancestors would paint either from boats or standing on ice. Using game technology, we can raise the water level to its original height in the digital model. This helps us to identify new potential sites around Lake Saimaa, for example, where more paintings might be found,” Miettinen explains.
“If we had permission to remove moss, even more paintings might be uncovered. It is not allowed to take paint samples from the paintings, and, in fact, the paint contains no substance that could be used for dating.”
The paint was likely an emulsion of sorts, with pigment mixed into egg white, fat or blood. The researchers have previously created and scanned various paint mixtures of their own in the university’s laboratory.
Paintings located at the same elevation on the rock face could, in principle, be from the same era. A similar shade of red paint, on the other, might be an indication of images painted by the same tribe.
Veikko Miettinen
Project Coordinator
Kimmo Katajala, Professor of History at the University of Eastern Finland, finds the research project fascinating, albeit somewhat outside his own field.
“I wouldn’t claim to be a specialist in this subject. My area of expertise pertains to Finnish history from the 16th century onwards, although I confess to having authored some works about the Middle Ages, too. These rock paintings date back much further. However, I’ve taken an interest because I’ve visited the petroglyph site on the eastern shore of Lake Onega, and that has led me to read up on these Finnish rock paintings as well,” he says.
“The rock carvings at Lake Onega were likely made 5,000 to 7,000 years ago. In other words, the technique is different from that used at Astuvansalmi, and the themes found at Lake Onega seem to reflect a more totemistic culture. The Astuvansalmi paintings portray elk, swans and boats – perhaps more representative of a hunter culture.”
“On the coast of the White Sea, there are also rock carvings clearly linked to a hunter culture. These depict, almost like comic strips, elk hunting on skis in the winter. Apparently, they are a few thousand years younger than the carvings at Lake Onega. The rocks on the coast of the White Sea also feature images of whales, boats, childbirth depicted with the umbilical cord, and male figures – many of them boasting an enormous phallus.”
“It’s interesting to note that the Northern culture of rock art seems to extend into Norway, where similar elk images as those found at White Sea, only painted, can be found as far up North as in Troms. I’ve seen those too.”
“Another intriguing thing is that no rock carvings are known west of Lake Ladoga – only rock paintings. So, there’s a clear divide in rock art techniques between the East and the West, although I’m not entirely sure where that line lies. I’m not familiar with any rock paintings or carvings between Lake Onega and Lake Ladoga in the Republic of Karelia in Russia: whether they exist and what they are like if they do.”
“So, what should we make of this merry mess of ancient paintings and carvings? I’m not entirely sure. Clearly, they represent different cultures in terms of their technique, painting versus carving, and in terms of their subject matter, totem animals versus hunting scenes. Although they share some themes – like swans, elk and boats – the cultures that created them may have been separated by thousands of years.”
Artificial intelligence can help reveal patterns worn down by time
Artificial intelligence offers new possibilities for analysing patterns in rock paintings. Recurring motifs might even reveal the distinctive style of a particular artist.
“Using neural networks, we can calculate and predict potential pattern similarities in rock paintings. The motifs at Astuvansalmi may resemble those found in Alta and Murmansk, such as people, weapons and animals,” says Research Director Dmitri Semenov from the School of Computing.
“Data analysis can take up to a year, and we’re supported in this work by students, with Master’s theses and doctoral dissertations already underway on the topic.”
“It’s certainly exciting if new images can be discovered using novel techniques. But when it comes to using AI to ‘fill in the blanks’ in existing motifs, I’d advise caution,” Professor of History Kimmo Katajala says.
“As far as I understand, AI does exactly what it’s trained to do. Rock paintings and rock carvings may be products of vastly different cultures and time periods. If the algorithm is trained on data from elsewhere, such as Alta or Murmansk, it will fill in the blanks based on those training data. If those data reflect a different culture or technique, the AI might misinterpret the image, or how to supplement it, leading researchers astray,” Katajala notes.
What matters most, however, is that rock paintings are digitally preserved. Exposed to the elements, they may not survive another thousand years.
Moreover, not everyone has the opportunity to visit the paintings at their physical site.
“Digital archiving ensures that paintings remain accessible to everyone also in the future,” Semenov says.
Virtual reality glasses using 3D technology are already used in museums. For example, at the Murmansk Regional Museum of Local Lore, visitors can use VR glasses to explore the Arctic undersea world from the perspective of mammals, birds and fish. They can even leave their handprint on a virtual display, just as our ancestors did on the rock thousands of years ago.
“Thanks to VR glasses, real rock painting sites can indeed be brought into museums,” Semenov concludes.
What kind of images were taken at Astuvansalmi?
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