Issue 110

Jan / Feb 2010

Contents

news

Burnt mound theory tested to perfection

Dig find proves flowers placed in bronze age graves

UK's first complete Roman lantern found in Suffolk

Research continues as Saxon hoard is valued at £3.3m

in the press

in brief & phase 2

features

Newhenge: Latest discoveries and interpretations from the Stonehenge Riverside Project team

Dig the beat: Exploring pop music from an archaeological perspective, including additional online content

THE BIG DIG Mellor: A hillfort in the garden: This long-running research excavation near Stockport, Greater Manchester, is now ready for publication

The Peat Men from Clonycavan and Oldcroghan: Findings of the Bog Bodies Research Project at the National Museum of Ireland, with Bibliography

letters

your views and responses

on the web

Caroline Wickham-Jones looks at archaeological gifts

Dan Pett summarises the website set-up and technologies for the Staffordshire Hoard

spoilheap

science

Cremated – but not silenced

Sebastian Payne, chief scientist at English Heritage, extols the value of ancient human remains that until recently were little considered.

It is easy to think that you cannot learn much from cremated bone. But appearances are misleading, and in the past decade there have been significant advances in working with this material.

When a body is cremated, the bones shrink, distort and break up, making it hard to identify a high proportion of the pieces. It is harder to tell male from female, because shrinkage is unpredictable; and hard to age adults closely because tooth crowns have shattered and other age indicators are scarce. But unexpectedly, unerupted tooth crowns often survive in good condition, so cremated children can sometimes be aged more closely.

Cremation deposits can tell us much about the funerary ritual. The lack of soil reddening at the burial site shows that cremation usually happened elsewhere. Signs of more than one individual in a burial suggest use of regular pyre sites: when bone fragments were gathered, bits of older cremations were included by accident. Usually a cremation deposit has much less bone than we would expect. An adult cremation typically produces around 2kg of bone, but at Roman Godmanchester, for instance, the average adult cremation deposit weighed a little under 800gm. The size of cremation deposits was unrelated to urn capacity, and less variable than one might expect – it seems people had a clear idea of what was an appropriate amount of bone.

Firing temperature was often unexpectedly high. Colour provides a very rough guide: black or brown bone suggests around 300–400°C and incomplete burning, while white or bluish bone suggests over 650–800°C. Bone cremated at higher temperatures has larger crystals of hydroxyapatite – the phosphate mineral which is the main crystalline component of bone. At Anglo-Saxon Mucking (Essex), crystal size indicated cremation at temperatures above 650°C; blobs of melted glass on bones suggested they sometimes exceeded 940°C.

Some 300–500kg of wood is needed to cremate a human body, and so most of the charcoal recovered in cremation deposits is likely to be from fuel. At Roman Brougham (Cumbria), alder charcoal was more commonly found with men and birch with women and children. Prunus charcoal (cherry, sloe, plum etc) was commoner where there was other evidence that the cremation had been a grand affair.

Remains of personal objects, plants or animals (presumably from food offerings) are often found with the human remains. Anglo-Saxon cremation burials might include horse remains, while Roman pyres are more likely to have featured chickens and pigs.

Cremated bone can be reliably radiocarbon dated. At first sight this is very surprising. The inorganic carbonate in unburnt bone usually gives dates that are much too young, presumably because younger carbon is incorporated by recrystallisation or secondary crystallisation of carbonate in the bone. For this reason, inhumations are dated using the carbon in the collagen; as collagen burns, it had long been assumed that you cannot date cremations.

However, consistent and reliable results have been confirmed after a decade of dating cremated bone. The original explanation was that the inorganic part of bone, known as bioapatite, incorporates a small amount of carbonate in the crystal lattice; it was argued that some of this carbonate remains after cremation, and could be dated. Current research, however, is suggesting that it is carbon dioxide that is being dated, absorbed either from the pyre environment or later from the atmosphere as the bone cools. Whatever the case, the dates appear to be reliable. A number of major dating projects in Britain, Ireland and elsewhere in Europe are in progress using cremated bone.

Thanks to Gill Campbell, Tom Higham, Simon Mays and Fay Worley.

More science

P Naysmith et al, in Radiocarbon (2007), 403–08

M Van Strydonk et al, in Lunula Archaeologia Protohistorica 13 (2005), 3–10.

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