Issue 93

March/April 2007

Contents

news

Police station had old rifles in foundations

Why did hunter-gatherers dig row of pits in Scotland?

Child's boot and bible found in chimney

Oldest cremation burials

Demand to rebury 'Druid' child

In Brief & Phase 2

features

Let the games begin!
Dan Garner and Tony Wilmot found footprints and a sword at Chester amphitheatre

The nomads of Wessex
Andrew J Lawson finds inspiration in central Asia

Heating flint in Boston Spa
Malcolm Barnes describes an intriguing community experiment

on the web

Recommended websites

letters

Views and responses

CBA news

Headlines from the CBA office

ISSN 1357-4442

Editor Mike Pitts

features

Re-enacting list prehistoric skills at Boston Spa

Malcolm Barnes explains why a community archaeology group in Yorkshire heated flints beneath a fire.

The Boston Spa and District Community Archaeology Group began with my plea in the parish newsletter in 1999, wondering if there were "like-minded enthusiasts" who would enjoy exploring local archaeology and history. We soon found a concentration of prehistoric flintwork in ploughed fields, which became the main focus of our excavation and fieldwork.

Each summer one of the group's monthly meetings is a reenactment event linked with some aspect of the fieldwork we have been doing. There are two aims – having fun and finding out how things work archaeologically. So reenactment has both a social and a serious side.

We have tried flint knapping, prehistoric and Roman cooking, "saddle-querning" and rock carving. All except the flint knapping proved surprisingly easy to do. Experts, or enthusiasts (being enthusiastic is usually why they have bothered to become expert) have sometimes joined in and helped, or pointed us in the right direction.

There have been pleasing spin-offs too, like observing the effects of heat and rapid quenching on sandstone river cobbles, which we found worked well as pot-boilers (fire-heated stones dropped into cold water). This enabled us to recognise them more confidently in excavations. Our prehistoric cooking reenactments demonstrated that leaving the flint pot-boilers in the fire for too long reduced them to small calcined pieces suited only for crushing and using, say, as burnt flint "temper" in pottery (what potters would call filler, to change the properties of the clay).

But it was the flint knapping that proved the biggest challenge, and was most closely linked to our archaeological fieldwork. Last July we decided to conduct a reenactment experiment to see if we could reproduce the conditions which might have allowed flint to be heat-treated in prehistoric times to improve its knapping qualities.

It is known that prehistoric flint knapping was sometimes facilitated by preheating the stone beneath a fire to make it smoother, less brittle and easier to flake. Was it a process of trial and error? Was it easily repeatable? John Whittaker (Flintknapping, University of Texas Press 1994) recommends pretreating flakes or tool blanks, rather than larger nodules of raw material, slowly heating them to 450–500 degrees Fahrenheit (230–260 degrees Celsius) and then slowly cooling them.

For our experiment we used good quality blacky-brown boulder-clay flint outcropping on the east coast, similar to the material encountered on the prehistoric flint site we have been investigating. We crudely knapped the blanks and heated them the night before the reenactment event, so that the temperature of the fire could be built up slowly (for safety reasons, gloves and goggles are recommended while knapping, unless you are wearing strong glasses; flint can be sharper than a surgeon's scalpel).

The fire burned for two hours and cooled slowly overnight. In that way we might avoid the problem of cracks and potlid fractures from rapid changes of temperature, the kind you sometimes see in flint from arable fields caused by freezing and thawing. Perhaps the prehistoric flint knapper could heat his flint at the same time as his evening meal and begin work the next morning in daylight!

We laid the knapped flakes and blanks on a bed of yellow building sand in a flat-bottomed 40cm square pit, divided into four quadrants with depths of 2.5, 5, 7.5 and 10cm respectively. An iron stake was driven in to mark the centre so we could find the quadrants later.

The flints were covered with sand up to ground level. Flint nodules were arranged around the central stake above ground so that these, unlike the flakes to be knapped, would be in direct contact with the fire.

We intended the nodules to be broken down by overheating so that we could crush them for use as temper in pottery. The fire, which extended beyond the edges of the pit, was built up gradually to a good hot campfire size.

Nodules placed directly in the fire
The next evening the calcined nodules of flint were sorted from the ashes by eye and by sieving. The reduced pieces were easily crushed with stones and further sieved to produce grains suitable for blending with clay to temper our imitation prehistoric pots.

Flint at 2.5cm deep
The sand had turned red. Pressure flaking these flints produced longer removals than from untreated flint and a glossy, silky surface was evident on the flake scars. This effect had not been present on the unscarred surface. The treatment proved useful, but at this shallow depth the heat had caused many potlid fractures.

Flint at 5cm deep
The sand above the flints in this section had turned red, but remained yellow below, providing a useful guide to heat penetration. The effect on the flint was excellent, with all the above benefits, but none of the problems of crazing or potlid fractures. It was possible to lengthen pressure flaked scars considerably, from a maximum of 4mm on an untreated flake to 8mm on one heated at this depth. This would be particularly useful when working on fine implements with thin sections, such as knives or arrowheads.

Flint at 7.5cm deep
The sand remained yellow. The effects on the flint were limited and of little benefit.

Flint at 10cm deep
There were no observable heat effects.

Heat treatment was particularly beneficial in improving pressure flaking at 5cm, the optimum depth for burying the flint beneath the fire. Admittedly, the experiment was observed empirically, rather than by using more scientific measures, such as a pyrometer or a temperature-controlled oven, and its repeatability would depend on an element of trial and error. However, as the aim was a realistic method which could work in the field rather than in the laboratory, we were very pleased with the results. It makes a practical reenactment activity, at once both entertaining and educational, which any group might try.

Malcolm Barnes is founder of the Boston Spa and District Community Archaeology Group (www.bsparch.org.uk). Thanks to Don Henson (CBA head of education and outreach) for pressure flaking flints and observations on heat treatment, and Anne Wright (group member) for flint drawings.

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