I have been working as a Conservation Assistant at the WSHC for nearly a year, and a large part of my role involves administration and financial processing. However, one of the more interesting and slightly unusual aspects of the job is the hands-on work I get to do as part of the Conservation and Museums Advisory Service here at the centre, and I have recently undertaken training to use the x-ray machine which we have in the lab. This is a complex process which requires stringent processes, records and maintenance checks to ensure the machine is used safely and functioning correctly. Regular use of the equipment is key to building experience and a ‘feel’ for the items being investigated and how to get the strongest images.
How it works
Inside the x-ray machine is an x-ray tube. A heated filament called a cathode sits inside the tube and accelerates high energy electrons at a metal target anode, usually made of tungsten, as the electrons strike the anode they interact with the atoms. In this process, which is called Bremsstrahlung (braking radiation), the electrons lose much of their energy and a photon x-ray is produced. X-rays are electromagnetic radiation of a short wavelength and high frequency invisible to the human eye, but possible to record on photosensitive film, known as x-radiographs.
The object to be x-rayed is placed on top of a cassette which holds the photosensitive film. On exposure the x-rays will penetrate through the object leaving the image captured on the film. The x-rays are partially absorbed, “attenuated”, by the denser materials such as bone or metal and pass more easily through soft material such as soil or skin. Therefore, the strength of the x-ray (KV) and the length of time the object is exposed for is adjusted for the type of material, size and condition of the item.
The photographic films then require a wet, chemical process similar to that used for black and white photographic film with a developer solution to reveal the image, followed by a fixer to secure the image and a wash to remove all chemical residues. This process takes around an hour and half and must be carried out in the dark room, with only red light, which can be a little disorientating at first!
Digital or computed x-radiography is well established and allows greater speed in reviewing and manipulating images. CMAS are actively working to move to digital, so watch this space!
How X-radiographs are used in conservation
X-radiography produces images on a 1:1 scale which allow the conservators to investigate the structure, manufacture or identity of an object. Small dark bubbles can indicate casting processes, the distinctive herringbone structure of pattern welding or wave formations of damascening are often clearly visible in x-rays, even when the surface of a blade is severely deformed.
Moreover, x-rays pass more easily through deteriorated materials and voids, these areas will appear darker grey or black compared to the brighter white of more stable areas. This can show up pitting, cracks and breaks assisting in the accurate assessment of the condition of items and their longer-term conservation requirements.
X-radiography is a non-destructive way of retrieving and revealing information and so it is commonly used in the primary stages of investigation.
Exciting and unexpected archaeological discoveries show how no evaluation process for sites is fool proof. What happens next shows how important cooperation and communication is, particularly for the County Archaeology Service, who are tasked with supporting development AND safeguarding heritage. The critical concept is “significance” – how important are the remains; what is their potential to inform us about the past? Rachel Foster, Assistant County Archaeologist reports:
In 2017 Wessex Archaeology excavated a new housing development north of Bitham Park in Westbury. I had requested this work as a condition of planning permission, based on limited evaluation results. Unexpected discoveries demonstrated the challenges faced by Planning Archaeologists in understanding the significance of archaeological sites based on the results of trial trench evaluation.
The 2018 National Planning Policy Framework states that local planning authorities should identify and assess the particular significance of any “heritage asset” that may be affected by a proposal. In line with this advice, we often ask for sites to be investigated before the determination of a planning application, so that we have that information. Evaluation usually this consists of geophysical survey followed by trial trench evaluation. The Wiltshire and Swindon Historic Environment Record which contains detail on archaeological sites, buildings and finds, informs our decision making.
Archaeological evaluation can feel like a game of battleships. When geophysical survey goes well, and reveals features that look like potential archaeology, we ask for trenches to be dug and the features investigated by commercial archaeologists. The aim is to understand the significance of the site by investigating features within the trenches, which is not always so easy: if geophysical survey has not been carried out or is unsuccessful, then trenches are placed either systematically or randomly across a site and there is potential to miss remains. Today, the trenching is usually a 3-5% sample of the development site but in exceptional circumstances, up to 10% may be carried out. That sample of trenching should find archaeological remains within a site and provide enough information to understand the importance, extent and significance of any remains. Results of evaluation will then inform our advice to the planning officer on the impact of the development on archaeological remains. Remains considered to be of national significance are likely to be preserved in situ and not developed, but other remains are likely to be investigate. Early knowledge about archaeology and its potential effect helps the developers manage their risk and adequately budget for excavation costs, as well as post-excavation work and publication.
The geophysical survey results at Bitham Park didn’t show much other than a few lines representing ridge and furrow remains across parts of the site and a few other possible linear features. This image gives an example of the greyscale plot of the geophysical survey results (magnetromotry).
Geophysical survey isn’t always reliable, so I asked for trial trench evaluation prior to determination of the planning application: in some cases, later ridge and furrow can hide earlier remains. As the geophysical survey indicated, there were remains of medieval/post-medieval ridge and furrow cultivation; however, my assessment that there might be more archaeology was correct. Archaeological features were discovered across several trenches, mostly concentrated in the western part of the site. They included ditches, gullies and pits containing small, worn pottery fragments from the early/middle Iron Age and Romano-British periods (150BC onwards). Nevertheless, the significance and extent of the remains could not be fully understood, so I asked for a second stage of evaluation to provide more data. The extra information would help me define an area for archaeological mitigation – the full excavation of important features. The results confirmed prolonged and intensive agricultural use from the medieval period (1066- 1540). This had truncated and displaced features and artefacts from the earlier Iron Age and Romano-British periods; however, theses features included and arrangement of post holes representing a possible structure (see trench locations of two evaluation stages below).
On the basis of the two evaluations I asked for an area of excavation within the vicinty of where the most significant archaeological features were recorded, in the western part of the site and along a north-south trajectory.
In advance of the housing development an initial area was stripped with contingency and here’s an aerial view of the site below, can you spot anything interesting?
With all this lovely sunshine in the last few weeks, it has been good to see so many people of all ages getting out and about in the great outdoors. I have been doing quite a lot more walking myself recently and it has reminded me how lucky we are in Wiltshire having so many monuments and historic places that are easily accessible and make great walks. Many of our sites and monuments are very impressive, give commanding views and are free to enter.
I have always enjoyed that physical engagement with the past that you get from climbing up to a steep ancient monument, such as an Iron Age hillfort, a castle mound or the top of the spire of Salisbury Cathedral. The physical exertion has always helped me to understand the scale of effort required by the people who built them and encourages enquiry about who, when and how the monuments were built.
I distinctly remember my first visit to Maiden Castle Hillfort in Dorset when I was 9 or 10, and after a steep walk the sense of discovery and wonder at the size of the ditches and banks. Several decades later, three of which as an archaeologist, I still get that same buzz about visiting these types of site, and what better way is there to get fitter and heather and explore our wonderful monuments at the same time?
Since 2007 the Wiltshire Council Archaeology Team has been organising annual archaeology walks each summer, usually to coincide with the annual Festival of Archaeology organised and promoted by the Council for British Archaeology in July and August. The walks, led by members of the Archaeology team have been very popular and have include places such as Avebury, the Stonehenge landscape, Littlecote Roman Villa, Barbury Castle, the Wansdyke, Adams Grave and Knap Hill and Oldbury Castle.
The very first walk I led as County Archaeologist in 2007 was one of the most challenging. It was a very rainy and wet Spring and Summer and the July walk to Avebury, Silbury and West Kennett Long Barrow was hampered by flooding, so much so that we lost some of the group as they weren’t wearing appropriate footwear to wade across the flooded Kennett on the way to the Long Barrow. Nevertheless, there was plenty to talk about at Silbury as English Heritage were in the process of repairing the Hill after a partial tunnel collapse some months earlier. The repair work was a great opportunity archaeologists to learn more about the monument and how it was built. The 2014 publication of the results by Historic England are fascinating.
This year for the first time in 27 years the Council for British Archaeology is taking a break from organising the Archaeology Festival. However, the County Archaeology team are still organising three exciting and diverse walks, one each in July, August and September.
Sunday 29th July - Iron Age Hillforts. Starting at Battlesbury, Warminster
Long before the Army started training on Salisbury Plain, and even before the Romans ruled, massive earthwork defences were created on the chalk downland. The edge of the Plain above Warminster has been sculpted to created massive hillforts over 2000 years old. Were these structures intended to defend ancestral lands, or to say "this is us”? Were they citadels, granaries, or temples? The hillforts enclose older remains – sites of burials and sacred places, so there may be more to them than defence and power. Join us as we explore these massive monuments and the landscape that they occupy, see how archaeology has deepened our understanding of the hillforts and wonder why, after so much work, one fort may have been abandoned before it was finished.
Sunday 5th August - Avebury World Heritage Site
Avebury is well known for having the largest Prehistoric stone circle in the world. However, the stone circle is surrounded by a range of other funerary and ritual monuments dating to the Neolithic and Bronze Age, some of which are unusual and unique. This exciting tour takes you through and between the monuments, exploring the monuments and their relationship with the landscape. The tour will take in the Avenue, Waden Hill and Silbury Hill amongst others and explore the reasons why the Avebury landscape has been designated as a World Heritage Site.
Sunday 2nd September - Oliver’s Castle Roundway Down Battlefield, Bromham
The Battle of Roundway Down was fought on 13th July 1643, when the armies of King Charles I and Parliament clashed on the hills above Devizes. Our walk will explore the battlefield and its importance, as well as its place in the wider landscape. Join us to find out why there were Lobsters on the battlefield, how the Bloody Ditch got its name and what occasioned Charles I’s only recorded joke. We might also explain where Devizes castle went.
We will also explore the remains of much older monuments, Oliver’s Castle Iron Age hillfort and associated burial mounds, which are testament to how our Prehistoric ancestors used this landscape for settlement, defence and ritual activities.
The walks promise to be interesting and stimulating events for all age groups. They all start at 11 AM on a Sunday morning and will involve walking for 2-3 hours. The Iron Age Hillforts walk may be a little longer (3-4 hours).
All our walks are free but you will have to book a spot as we have a limit on numbers.
CMAS are excited to be working on the conservation of two Roman copper alloy items recently excavated by Foundations Archaeology.
The site at Cholsey, South Oxfordshire is thought to be an Iron Age settlement which evolved into a Roman Villa site. The villa buildings have been preserved in situ, but excavations were carried out on almost 2 hectares of land surrounding them.
The excavations revealed numerous burials and enclosures including a number of impressive corn driers.
Interestingly the archaeologists propose that the site was a prosperous farm that evolved to a villa, unusual as villas were more commonly set up by representatives of the empire.
CMAS are conserving a copper alloy necklace with a circular pendant, possibly made from bone, and a large copper alloy bowl.
The bowl was found upturned within the base of a corn drier, on top of charcoal deposits.
The backfill from the demolition of the corn drier was deposited on top of the bowl. This shows that the bowl was deposited at the time that use of the drier ceased, possibly as a closing offering and that this was done at the same time as closure of the site, not at a later date.
At the end of August I celebrated five years with the archaeology team here at the History Centre in Chippenham. I thought this a suitable milestone in which to reflect on some of the most exciting discoveries in the central part of Wiltshire (the area I cover), discovered through the advice we give on planning applications.
The Government set out its requirements for the planning system in the National Planning Policy Framework in 2012. Section 12 deals with conserving and enhancing the historic environment. The advice we give on planning applications follows this guidance which needs to be relevant, proportionate and necessary. It is important to understand the significance of heritage assets impacted by development, which is why we ask for a proportionate level of investigation to be undertaken prior to determining applications. Various stages of investigation are carried out. To begin with an archaeological Desk Based Assessment (DBA) pulls together existing information, using as a baseline the Historic Environment Record and other sources where available such as historic maps, aerial photographs, field surveys and site assessment. The DBA helps to establish the potential for archaeological remains to be present within a development site. Sometimes, there is little existing information available because there have been few investigations within the area. In such cases geophysical survey is a useful method for revealing unknown archaeological remains within a site. We get greyscale plots and interpretation plans to help understand what potentially is of archaeological origin. In most cases we ask for trial trench evaluation following geophysical survey. Trial trenching enables us to understand the significance of the archaeological remains which will be impacted by development. Depending on the heritage asset’s significance (to use NPPF terminology) we may ask for a site to be preserved in situ i.e. not impacted by development, or preserved by record i.e. it gets excavated, the remains assessed and then reported and/or published. The following examples show previously unknown settlements which have been found through such methods.
Westbury Trial trench evaluation followed a geophysical survey in 2015 which discovered a number of features dating to the Romano-British period including a number of trackways and ditches. The site has yet to be developed.
Melksham Trial trench evaluation followed a geophysical survey in 2014 which confirmed the presence of a Romano-British settlement. The site is currently being excavated, more detail to follow.
At another site in Melksham, a geophysical survey identified a number of features and the trial trench evaluation confirmed remains dating to the prehistoric, Roman, medieval and post-medieval periods. The site has yet to be developed.
Trowbridge Geophysical survey across a large proposed development site highlighted two sites of particular interest. Trial trench evaluation confirmed a concentration of early Romano-British ditched enclosures associated with trackways and pits and posthole features which appear to represent settlement remains. The relationship between the two sites is of interest. More ephemeral prehistoric activity was represented in other parts of the site which the geophysical survey did not pick up.
I have written before about some of the amazing finds at the site that will become the Larkhill Service Family accommodation. Archaeologists from Wessex Archaeology and White Young Green have been ensuring that the archaeology has been excavated, with archaeologists from the Wiltshire Council Archaeological Service (mostly me!) helping to ensure that anything affected by the development is properly excavated and recorded. We’ve had Neolithic, Bronze Age and Iron Age finds, including a Neolithic causewayed enclosure, a new (probable) henge and an enclosed settlement (with associated roundhouses). I’ve also mentioned before that we have the remains of a First World War training battlefield, with what has turned out to be over 8km of trenches that have been excavated by the archaeologists and unexploded ordnance specialists that have been working on the site (an example of some of these trenches are shown in this picture – the trenches are white from the excavated chalk being backfilled into them. The second photo shows part of the trench system).
In addition to the trenches, we can now reveal that the practice battlefield also included tunnels and dugouts. On battlefields, dugouts were used for lots of reasons, including troop shelters, medical posts, headquarters and stores. Their position underground meant that they were less likely to be affected by bombs, shells or bullets. We have a number of these at Larkhill, along with a number of tunnels. Both sides dug tunnels into no-man’s-land in order to lay mines that could blow up the other side’s trenches. Counter trenches were also dug to try to stop this. Tunnels were also used as listening posts (listening for the sound of the other side’s digging).
(These pictures show the entrance to one of the dugouts, with steps leading down, and another with a cob wall and doorway forming a room inside.)
The presence of these tunnels and dugouts (along with the trenches, ammunition, grenade fragments and food containers – amongst other things!) show that the troops training here were learning to undertake all aspects of trench warfare. They may well have come from all over the Commonwealth, but we know for a fact that we have people from the Wiltshire Regiment, drafted West Yorkshire coal miners, Manchester Scouts and troops from Australia. We know this thanks to the over 100 pieces of graffiti that have been found written on and carved into the chalk of the defences. Sometimes the graffiti was written in soot from candles, but more often if was written in pencil on the chalk.