Burnt bone in Structure Eight and beyond – adding fuel to the fires?

By Jackson Clark

Jackson Clark on site in 2024 with his demonstration hearth. (📷 Sigurd Towrie)
Jackson Clark on site in 2024 with his demonstration hearth. (📷 Sigurd Towrie)

Since the close of the Ness of Brodgar this past August, the focus has shifted towards investigating the massive quantity of material collected over the last 20 years. At the undergraduate, masters, and professional level, students and professionals alike are beginning to make a dent in that workload.

In the spring of 2023, I joined the project to investigate burnt bone. This project was brought on by the sheer volume of a usually footnoted material type. The questions we asked were two-fold: (1) what can we learn about burnt bone, and (2) why is there so much of it at the Ness of Brodgar?

As of December 2024, my MRes program at the Ness has finished and I am back in America. But my brief study into burnt bone has revealed a number of unique facts about the ways Neolithic Orcadians lived.

With the help of UHI Archaeology Institute zooarchaeologists Dr Ingrid Mainland and Dr Julia Cussans, I inspected a total of 5,567 faunal remains from Structure Eight over the course of my degree. Of those, only 571 were identified to a species level. Why is that?

To explain why only a bit over ten per cent of the assemblage has species designations, we have to talk about what fire, especially at high temperatures, does to bone.

Hydroxyapatite, or bone, is a composite material with both organic and mineral components. Fire burns away the organic material and compromises the minerals, effectively shrinking and morphing bone which make identification harder. And while burnt bone is less likely to dissolve in acidic soil or water-heavy environments, it’s significantly more brittle and fragments at a much higher rate.

The result is a collection of small, mostly sub-centimetre fragments where identification is much harder.

Burnt bone condition chart
Figure 1

What we found in Structure Eight was a highly combusted assemblage of animal bones. More than half of the faunal remains in Structure Eight were burned to some degree, with most bones falling into a category of burning called “calcined” (Figure 1). These represent the most severe degree of burning with temperatures well beyond those we’d see in a cooking setting.

As temperatures get more intense, bone goes through a variety of changes in both colour and structure. What may start as a pale beige or “bone white” unburnt fragment first blackens (or carbonises) at around 300 degrees Celsius then calcines, turning pure white, at around 700+ degrees Celsius. What this means for our assemblage is that these bones were not burnt in an ordinary fashion purely for consumption.

Broken cattle tibia shaft fragment that has been calcined. (📷 Jackson Clark)
Broken cattle tibia shaft fragment that has been calcined. (📷 Jackson Clark)

As a consequence of more than three quarters of the Structure Eight burnt bone being calcined, our fragments were incredibly small (an average fragment size of 2.41 centimetres). In turn, identifications became much more difficult. So, what do those 571 fragments tell us about Structure Eight? Quite a lot, actually.

To begin, we’re seeing a clearer picture of how animals were treated at the Ness. Neolithic Orcadians relied heavily on two main animal resources: cattle and sheep. Since we started looking at animal bone at the Ness, we’ve known how incredibly important cattle were to people there; it’s the only Neolithic site in Orkney where cattle outnumber sheep.

Fig 2.

Figure 2 shows the distribution of different skeletal parts compared to what would be expected of a full carcass. The blue line is the expected proportions of four different skeletal groups, those being the upper portion of limbs, the lower portion, the feet, and the jaw. The orange and green lines show how cattle and sheep from Structure 8 compare to those expected values.

What this graph tells us is that Structure Eight bones indicate whole cattle are being taken to the Ness, as that line very closely follows expected values of a whole carcass. Conversely, it would appear that the sheep found in Structure Eight are being brought in parts – specifically that they’re bringing common cuts of meat on-the-bone. That pattern is unique among Neolithic Orcadian sites!

Calcined sheep proximal ulna (left) and distal humerus (right); these elements articulate, with the circular distal humerus connecting with the groove found on the ulna. (📷 Jackson Clark)
Calcined sheep proximal ulna (left) and distal humerus (right); these elements articulate, with the circular distal humerus connecting with the groove found on the ulna. (📷 Jackson Clark)

When those species categories are further broken down into their burnt and unburnt components, another interesting trend emerges. Figure 3 shows the same sort of element breakdown, with upper and lower limb categories (think shoulder and hip vs. forearm and shin) as well as feet and jaw categories. However, this graph breaks down the cattle into the burnt and unburnt categories.

Fig 3.

The story this graph tells is that Neolithic Orcadians are disproportionately burning limb elements. Those limb elements are where most all the cuts of meat we regularly eat are located (save for a rack of ribs). Burning food-bearing elements at such high temperatures is clearly not to cook them. Which once again begs a question: Why?

Any regular reader of the Ness of Brodgar daily diaries is likely intimately familiar with our famous middens, particularly the Central Midden Area. What is so interesting about these burnt bones most likely has to do with the middens themselves.

Calcined cattle first phalanx proximal articular surface next to comparative specimen. (📷 Jackson Clark)
Calcined cattle first phalanx proximal articular surface next to comparative specimen. (📷 Jackson Clark)

Most of the Structure Eight burnt bone (nearly 90 per cent) comes from midden infill that was used to seal the building after it had fallen out of use. In many ways, archaeologists function as ancient dumpster divers and middens are our ultimate prize. Midden can be many different things, but most often they are organic-rich deposits of sediment that are essentially trash heaps. This midden surrounded most of the buildings, including Structure Eight. That pile of meterial is very convenient when trying to fill in a building with sediment so you can rebuild atop new ground.

Aligning these seemingly disparate facts, a clear interpretation emerges. We have extremely burnt, high meat-utility bones being found in trash heaps. One of the more logical interpretations is that Neolithic Orcadians were burning their trash.

Experimentally burnt bone showing carbonised (in black) and calcined (white near bottom) on a continuous spectrum (i.e. the fire was hotter closer to fuel and therefore bone calcined, while black bits were more removed from highest temperatures). (📷 Jackson Clark)
Experimentally burnt bone showing carbonised (in black) and calcined (white near bottom) on a continuous spectrum (i.e. the fire was hotter closer to fuel and therefore bone calcined, while black bits were more removed from highest temperatures). (📷 Jackson Clark)

Growing up in communities with wood-burning stoves, practically everything that could go in there did; simpler to clean out ash than bother with rubbish bins. In this way, I’d contend the people of the Ness weren’t much different. Keeping warm in the harsh North Atlantic winters likely demanded some fires specifically for heat, not for cooking. Those would ostensibly be hotter and more likely to reach the temperatures necessary to calcine bone.

The story of the Ness will continue to grow as more post-excavation research is completed. Indeed, Structure Eight cannot stand in for the entirety of the Ness of Brodgar’s burnt bone.

But more faunal assemblages are currently being studied and in due time, we’ll be able to tell a lot more about the Ness than one building’s rubbish practices.

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