Investigating the Stone of Destiny through science and technology

Specialist techniques, science and technology are essential in the conservation of Scotland’s heritage, including the iconic Stone of Destiny.

Also known as the Stone of Scone, the Stone of Destiny is one of the most important symbols of Scottish nationhood. This rectangular-shaped piece of sandstone, quarried in the locality of Scone, was the seat of Kings of the Scots until John Balliol (1292) and monarchs of England and the United Kingdom thereafter. Most recently, it saw the coronation of King Charles III.

When preparing for the coronation, which required moving the stone from Edinburgh Castle to Westminster Abbey, three teams of specialists within Historic Environment Scotland – Applied Conservation, Heritage Science, and Digital Documentation – had unprecedented access to the stone to:

• check its condition and treat it
• analyse its composition to understand its condition better and make informed decisions about its conservation
• create a 3D digital record

Our latest report, The Stone of Destiny: condition assessment, scientific analysis, and digital documentation 2023, details this innovative and meticulous work in detail. In this blog, explore five of the major results of these teams’ efforts when conserving the Stone of Destiny.

Roman numerals and incisions

Together, using a combination of detailed condition assessment methodologies, and different visualisation methods, these teams discovered and then analysed a previously undocumented incised inscription on the stone. The inscription resembles roman numerals or letters: XXXV or possible XXXVX with the last ‘X’ being slightly larger.

Specialist stone conservators, when carrying out the condition assessment, carefully assessed the stone and its structural stability, surface condition, and features. They did this using both the naked eye and a portable microscope in different light settings including UV light. Using these techniques led to the discovery of the incision.

Experts in digital documentation and 3D visualisation were able to modify photographs of these incisions so they could be seen more clearly. The investigations of our heritage scientists meanwhile, revealed the incisions to be ~1mm in width, suggesting they were made with a very fine chisel or cutting instrument.

It is possible these markings are from the twentieth century, either during the Second World War when the stone was concealed for safekeeping, or the 1970s after a second, failed attempt to remove the stone from Westminster Abbey.

Hidden fibres

The stone bears a more definitive trace of the reaction to that attempt in the 1970s. On its back face, there is a small, slightly off-colour circle; a repair of a hole found in 1996. It previously held a small, lead tube with an offcut from a 1970s authentication document (accession number E6120), which had been covered with a wax seal.

Under UV light, thread-like fibres can still be seen, thought to be gauze or paper.

Caption: Lower-right corner of the back face of the stone under UV light, showing the area where the lead tube and wax seal used to be, and thread-like fibres remain.

Elemental traces

Analysis from our Heritage Science Team, including portable x-ray fluorescence (pXRF), revealed the chemical element composition of the stone and its surface, and what this tells us about its life and use.

pXRF analysis was able to confirm research from 1998 before that technology was available. Scientists confirmed the stone is a non-calcareous litharenite (a stone that does not contain calcium carbonate, and contains >5% of lithic fragments—pieces of rock which have eroded into sand grains).

The team found evidence of sulphate (SO3) and calcium oxide (CaO), which indicated the presence of gypsum (CaSO4.2H2O). Gypsum is a soft, grey or white mineral. The source of the gypsum is not known.

Did you know that arsenic was used in paint pigments? The back and Sinister (left) surfaces of the stone have isolated instances of slightly elevated concentrations of the element, and our scientists think this came from pigments used in paints known to be on the Coronation Chair. Traces naturally transfer between objects that come into contact with each other, and analysis like pXRF carried out by experts find these traces and help make sure that people who work with those objects manage any associated hazards. After the stone was transported from Edinburgh Castle to Westminster Abbey, it was then moved to its new home at Perth Museum near Scone.

It takes a lot of planning and care to transport an object like the Stone of Destiny. Levels of chromium discovered suggest that tools used at some stage caused minute trace transference. This could have happened at any time in the 20th century, possibly even in the 1950s. Recent moves have avoided the use of such tools and reinforce the need to move objects such as this only with trained handlers and conservators to ensure their safe movement.

The Stone of Destiny leaving Edinburgh Castle for the first time in more than 25 years for London for the Coronation of King Charles III.

3D model and print

Heritage is for all, but handling some objects too much can be harmful over a long period of time. Thanks to our Digital Documentation and Innovation Team’s world-leading expertise in 3D data capture and visualisation, they were able to create a highly-detailed digital 3D model of the Stone of Destiny.

The team documented the stone using a technique called photogrammetry: the process of taking hundreds of photos from many different angles and feeding them into specialist software to generate a photorealistic 3D model. The Stone of Destiny took a total of 862 photographs to capture in full, using a DSLR camera with 35mm, 50mm and 90mm lenses.

Digital Documentation Officer David Vacas Madrid photographing the Stone of Destiny in the Crown Room at Edinburgh Castle.

At the castle, the team was careful to capture every side of the stone, positioning it on different faces so as not to miss out any angle. These different sides could be brought together back in the office through the use of common reference points, or ‘targets’, that can be seen surrounding the stone in the above image. In order to ensure the virtual stone looked as close to real life as possible, the team used a number of techniques to ensure accurate colour information was captured from the real stone to the camera, including tonal and white balance adjustments. These steps result in a 3D model where the colours are near indistinguishable from the real stone to the human eye.

The outputs from the digital documentation of the stone include:

• High resolution 2D images to aid in monitoring and conservation of the stone
• A shareable 3D model which is virtually accessible, meaning more people can see the stone up close
• An accurate record of the stone’s condition at the time of documentation
• A 1:1 scale 3D print replica that helped the teams with planning the movement of the stone, and has been used as an outreach and engagement tool

To find out more about the work of all of our specialist teams who worked on the Stone of Destiny, download our new report now.

The Heritage Science team also published a report of a fragment of the Stone of Destiny. Or read the Edinburgh Castle Statements of Significance, which include the Stone of Destiny. And, of course, if you are in Perth, drop by Perth Museum to see the Stone of Destiny for yourself.

Learn more about our Digital Documentation and Innovation Team and our Heritage Science Team.