Elaborately carved with patterns of spirals, circles and wandering lines, smooth curves and distinctive ‘knobs’, it would look perfect as a garden decoration, a paperweight or on a windowsill.

And, indeed, a window ledge is where one of Scotland’s most enigmatic and intriguing objects was apparently found: a carved stone ball rooted in prehistoric times, unearthed by curious fingers, dusted down and admired enough to be given a fresh use as a household ornament.

It was one of more than 500 Neolithic carved stone balls, some with intricate patterns, others with expertly carved knobs and tiny pyramids – some may even say they have an intriguing similarity to the Covid-19 virus with their circles and spikes – to have been found in Scotland, and which have sparked endless debate about what exactly they were used for.

Now, a fresh effort is underway at the National Museum of Scotland to unravel the meaning behind Scotland’s 5,000-year-old carved stone balls. It involves a fingertip search through hundreds of documents cataloguing their discoveries, virtual reality technology, citizen science and a hunt for at least two missing balls - and perhaps many more.

Most of the intriguing stones were discovered in Aberdeenshire, however, in many cases precisely where they were found was either not fully recorded or the spheres mistaken as either not being as historically important as they are now known to be.

As a result, it’s thought that some may not even have been handed over to authorities as archaeological treasures – meaning there is every chance that they are still kept by unsuspecting owners, have been sold, forgotten about or, indeed, stuck on a window ledge.

Now Dr Hugo Anderson-Whymark, Curator of Prehistory at the National Museum of Scotland, is at the forefront of a new strand of research which it is hoped will unlock the secrets of the intriguing Neolithic objects and possibly the whereabouts of at least two missing spheres.

“We are on the trail,” he says. “We’re working on trying to track down a couple that are known to exist, one was last seen in 1896, the other in 1908.

“And there are probably a few that were found and taken away because people didn’t know what they were.

“Scotland’s Treasure Trove (system) means every archaeological find should be reported. The law now is the same as it has always been, but in the early 19th to 20th century no one was enforcing it.

“So, a lot of things are in private hands.”

One missing stone came to light after the original finder realised four decades too late just what he had had on his hands. It was only when he noticed the object’s similarity to a carved pinkish red sandstone ball found on the floor of House 8 at Skara Brae in Sandwick, Orkney by Prof. Vere Gordon Childe in 1928, that he made the connection.

“He realised 40 years after he’d given it away, and it was sold as part of his cousin’s estate when he died,” adds Dr Anderson-Whymark, who will present a University of the Highlands and Islands Archaeology Institute online seminar on his research next Friday.

Another missing ball appears in a photograph which was shared with the museum by a collector, who confirmed they had not been able to obtain it. Its current location remains a mystery.

However, there’s every chance others may be dotted around the country.

“We have references of them being found on someone’s window ledge,” he adds. “It’s the kind of thing that, if you found it in the ground, you’re not going to leave it there. You’d pick it up and take it with you.”

The stone spheres are typically around three inches in diameter. Most are carved with three distinctive ‘knobs’, although some can have many more. While some are highly decorated with swirls, spirals and tiny carved pyramids, others appear rough and barely finished.

One of the finest is the Towie ball, sculpted from black, fine-grained stone, which has four distinctive discs carved into its surface, three of which are intricately carved in mesmerising patterns, the other left completely blank.

It was discovered when a deep drain was cut underground on the slopes of Glaschul Hill, Towie, in Aberdeenshire around 1860.

The most recent carved stone ball was found in 2018 during work being carried out to plant trees in Perthshire. The location was later excavated and revealed a scattering of flint tools and other carved stones.

Carved stone balls found during excavations of the Neolithic site at Skara Brae in Orkney helped debunk suggestions that they were produced much later and added to the intrigue over how they were made and why.

Various possibilities have been suggested, from weights to weapons, ritualistic objects to apprentice pieces displaying the crafter’s skill.

One theory suggests they were used at tribal gatherings as 'speaker stones' - held by those with the right to address the group. It has also been claimed the carvings recorded historic events and were used as mnemonic aids in the way Australian Aboriginal cultures used rock art.

Patterns and shapes on the spheres have also been found on mace and axe heads and are also echoed in rock art found across Scotland.

“They have captured people’s imagination and they are not short of interpretation,” adds Dr Anderson-Whymark, whose research involves exploring the Museum’s three extensive catalogues which detail hundreds of stones found at locations across Scotland from the mid-19th century onwards.

Meanwhile, 3D models of the carved stone balls held in the National Museum of Scotland’s collection have opened the opportunity for them to be explored remotely and using virtual reality.

It is hoped that will encourage amateur detectives and archaeology experts around the world to add their thoughts to the debate about their use.

Analysis of the stones suggests many have been reworked several times down the years, and possibly passed through the hands of several generations being altered on the way, says Dr Anderson-Whymark.

It raises the suggestion that they may have started out having one use and evolved to become another.

“We can see with some that they have potentially very long periods of manufacture and were not simply made to that finished form in one go,” he adds.

“They might have started as a plain stone sphere, they might have some knobs carved on the surface and they might have been quite shallow.

“At a later date, they made them deeper, or they might have decided to change the design entirely - we see on some the pattern is entirely changed and reworked from six knobs on surface to dozens.”

The idea of the spheres being passed through generations raises the idea that they may have been an ancient form of ‘heirloom’.

“There’s a division between what we see now as a practical object and a ceremonial object, but those divisions were not the same in the past,” he adds. “It could be that the carved stone balls held multiple functions and could be ceremonial and weapons at the same time.

“Or if they were around for several hundred years, they could have started out as one thing - say weapons - and ended up as more ritual items and status items of prestigious members of the community.

“Their use can change over time,” he adds. “In my opinion there’s not one correct answer.”

For details of The University of the Highlands and Islands Archaeology Institute online seminar, go to https://www.uhi.ac.uk/en/media/events/