Skip to main content

About CU ConservationObjects and TreatmentsStudent's Stories

Conserving Viking Archaeology Part 1: The Batch Treatment of Iron Finds from the Site of the Great Army Encampment at St Wystan’s Church, Repton

4 January 2023

In 865, The Great Army, a 3000-strong pan-Viking force, arrived on the Kent coast.

According to the Anglo-Saxon Chronicle, the force reached Repton, Derbyshire in 874, and established a long-term camp. Once the Mercian king fled the country, the Vikings took control of Mercia, and later incorporated East Mercia into the Danelaw. Until recently, contemporary writing was the only evidence such a camp had existed.

Digs around St Wystan’s Church in the 1970s uncovered remains of Viking burials and a defensive ditch resembling those found in Scandinavia.

Further excavations were carried out in 1998, 2016, and 2018 to gauge the nature of Viking influence on the surrounding area. These uncovered many objects dateable to the late ninth and early tenth centuries.

Six other conservation students and I were lucky enough to treat metal finds from these digs while on placement at Cardiff University. This blog series goes behind the scenes at the lab, looking at how conservators contribute to discoveries we make about the past from the evidence hidden beneath our feet.

Four students wearing white lab coats are standing around a long tablet covered in cutting mats and a large lightbox. A box containing many bags of corroded iron objects in open in front of them. There is a notebook open on the table, a list written on the pages.

Image: Emma, Sorcha, Tessa and Courtney (left to right) inspecting and sorting the iron finds.


The Finds

Most of the objects were iron, many encased in thick layers of corrosion making them impossible to identify with visual inspection alone. These had been X-rayed by a previous student cohort hoping to pin down their appearance and likely function from the shape of the uncorroded iron core. However, further progress was hampered by restrictions during the COVID-19 pandemic.

A block of six photographs of X-rays of iron objects, mostly nails, but also some buckles, hooks, lock shackles, blades and interestingly shaped fittings. The X-rays are labelled: J917; J918; J919; J920; J921, and J922.

Image: Photographs of the X-rays of the iron finds taken by the class of 2019-20.


Treatment Stage 1: Batch Consolidation

As we checked through the boxes, we found a few finds in worse condition than they had been two years earlier.

Three students wearing lab coats sat around a table. One student does a task out of frame; the two others sit at opposite sides of a lightbox viewing an X-ray.

Image: Students viewing the X-rays using lightboxes. Background: Courtney. From left to right foreground: Emma and Tessa.


The X-ray shows object 70519 was a nice example of a hairpin.

An X-ray image showing the core of a long pin with points at both ends. The object is labelled '70519' in white pen.

Image: Photograph of the X-ray image of object 70519.


It is now in three long pieces, the laminating layers of corrosion having pulled away pieces of the remaining iron core. This leaves the core exposed to oxygen and moisture, which cause further rusting.

Many small fragments of an iron object covered in lumps of brown corrosion spread out on a piece of blue roll. Three larger long fragments at the bottom of the image show the surviving main body of the object.

Image: Object 70519 after two years in storage. The plastic-like coating is the result of consolidation, which is discussed further below.


In these circumstances, it was necessary to consolidate all the finds before further handling or treatment.

We made up a solution of 5% Paraloid B-72, an acrylic adhesive, in acetone and poured just enough into glass dishes to cover the bottom of the finds. We placed these under a vacuum, which drew a thin layer of solution over the objects. This consolidates objects thoroughly while avoiding imparting a shine.

A woman with long brown hair in a white coat pours a liquid into a glass container standing on an electric balance inside a fume cupboard.

Image: Leonie pouring out the enormous volume of acetone necessary
to make up enough of the 5% solution needed to consolidate all the finds.

A woman wearing a lab coat with red hair tied back from her face smiles while holding up a small square cloth bag. She stands in a lab in front of a fume cupboard and behind a set of drawers.

Image: Courtney modelling the huge mesh bag I stitched
to suspend the beads of Paraloid B-72 in the acetone to form the
adhesive solution.

Three Pyrex dishes on a table with iron objects covered in brown corrosion laid out inside them. Sheets of paper beneath the dishes show the position, shape and find number of each object. The objects sit in a very shallow pool of clear solution.

Image: Some of the finds in glass dishes before the solution was added and they were placed under vacuum.

A large green-grey box in the corner of a room with a large round metal door and a row of five dials along the bottom. Through the circular window in the door, a dish covered in tin foil on a shelf is visible.

Image: Our lab vacuum box chamber with trays inside. The tin foil covering prevented
the acrylic solution from being drawn out of the tray under vacuum.


After allowing excess solution to run off, we placed the finds on silicone release paper inside fume cupboards to dry and allow the acetone to evaporate off safely.


Ethics and Aesthetics: Prioritising Objects for Cleaning and Further Treatment

Small iron archaeological finds are typically cleaned using air abrasion. This involves firing powder particles at high pressure at the surface of an object, using a unit like those used in dentistry. This removes layers of dirt and corrosion, revealing the object’s original shape, in a slow, controlled manner, reducing the risk of breakage.

Conservators normally remove corrosion down to the magnetite layer, a dull grey to black corrosion layer close to the metal core. This allows the shape of the original object to be revealed without exposing the reactive pure metal core to oxygen and water.

Hand-drawn diagram showing a cross-section made up of three distinct layers. The top layer is red-brown, uneven and full of extraneous matter represented by circles. This is labelled 'iron (III) hydroxide oxides (rust) + soil particles'. The middle layer is more even, shaded with lines and coloured in dark grey. It is labelled 'magnetite (Fe3O4)'. The final layer is labelled 'iron core', and is coloured light grey.

Image: Diagram (author’s own, 2022, based on Selwyn 2004, p.106) showing the layers making up corroded archaeological iron objects. The magnetite layer forms closely over the original iron surface.


This is a time-consuming process. To clean the over 100 iron objects entrusted to us would require resourcing and a timescale rarely available to even full-time professional conservators. Across conservation, it is necessary to prioritise the treatment of certain objects over others. This guarantees that the maximum amount of information is extracted.

My classmates and I made a shortlist of fifteen finds that we found particularly ‘interesting’.

A list of object numbers handwritten in a notebook with the title 'Interesting'. Some numbers are circled and/or have lines struck through them. Next to the number 70519 is written 'Mine!'

Image: Our list of ‘Interesting’ objects, using their find numbers. As the key shows, circled numbers denote finds selected for the ‘super cut/high priority’ group (see below). ‘Mine!’ is next to find 70519, the corroded hairpin, because I was determined it could be saved.


These were finds we recognised from the X-rays taken by the previous students as uncommon in the context of the site and wider excavations of early medieval British sites.

A lump of metal in the shape of a lock shackle covered in a thick layer of brown corrosion. There is a ball shape one end followed by a large heart-shaped chunk of corrosion. On the other end there is a long tapering rectangular shape reaching half way up the prong of the shackle.A long elliptical object with a hollow in the middle and a small rectangular handle, resembling a scoop. The object is covered in dark brown corrosion. A large, roughly 'C' shaped metal bar resembling a handle, covered in brown lumpy corrosion.

Image: (top to bottom) lock shackle; small scoop; handle. All are covered in a thick layer of corrosion.


For example, we chose a shackle of a padlock, a little scoop, and a handle. Cleaning these could reveal more about their purpose, and therefore information about contemporary technology and daily activities and uses of the site, than objects more common on this and other sites, like a nail.

This large bolt was also selected, as it was unique among our finds, and could evidence larger-scale construction taking place.

A large bolt with a tapering point on one end and a rounded head at the other with a hollow in it, covered in laminating layers of dark brown corrosion. A separate flake covered in similar corrosion products sits above it.

Image: Photograph of the large bolt, and a corroded fragment that had come away from the main object.



We also identified thirteen finds that were potentially interesting, but the X-rays had not revealed their shape in sufficient detail to be certain.

A list of finds numbers, corresponding X-ray film sheet numbers and comments on the success of the X-rays handwritten on lined paper titled 'Re X-ray'. Find 70519 has the word 'Lost' written and a sad face drawn next to it.

Image:Our list of find numbers to be x-rayed again, featuring notes on the issues with the previous x-ray to help us decide on kVs and exposure times for the new X-ray. Find 70519 was the hairpin was initially declared lost until consultation with Phil Parkes suggested it could be saved.


For example, the first X-ray suggested find 70438 was a curved iron bar.

Photograph of an X-ray of a curved bar seen along one edge.

Image: Photograph of the first X-ray of find 70438.


However, this photograph of 70438 (below) shows that the X-ray (above) does not reveal as much about the construction of the object’s ridged spine as X-rays from other angles could.

Photograph of a curved iron bar viewed from an angle showing the convex side and one edge. The bar appears slightly ribbed along the convex side, though the overall shape is obscured by dark grey and brown-green corrosion products.

Image: Photograph of find 70438.


We X-rayed these finds again at a higher kilo voltage (kV) and longer exposure time, and 70483 from different angles.

A student in a white lab coat arranges iron objects beneath lead letters spelling out 'K23' on top of a sheet of paper over an X-ray film guard on a white worktop. Two students in lab coats, one in the background with red hair tied in a bun, and one in the foreground with chin-length brown hair and glasses arrange iron finds and lead letters on a paper of paper overlaying an X-ray filmguard.

Image: Leonie (left), Courtney (right background) and Tessa (right foreground) arranging finds and lead letters over the X-ray film.


A student with long dark brown hair in a ponytail wearing a white lab coat places an iron object on a black X-ray filmguard on top of a sheet of plastic into an X-ray machine, an oven-like device, through a door open from the top.

Image: Lexie preparing to take a new X-ray.


The new X ray revealed that find 70621 had a deliberately made hole in the middle. This suggests it is not waste material from the manufacture of another object, but had its own function. 70583’s believed bolster or cross-guard was revealed to be dense corrosion near a contact point between two different metals, shown by the difference in brightness.

A plate-like arc-shaped flat object covered in light brown corrosion products.An object resembling a small knife covered in lumpy dark brown corrosion.

Image: Photographs of finds 70621 (top) and 70583 (bottom).


A photograph of an X-ray of find 70621, revealing a round hole in the centre right of the object.A photograph of an X-ray of find 70583. The tapering end of the object is dark grey; the broader end is pale grey, almost white. Clouds of dull grey material surround the wider end of the dark grey section of the object.

Image: Photographs of one of our new X-rays, showing the hole in find 70621 (top), and 70583’s bimaterial composition (bottom).


70483 was revealed not to be a solid bar, but a loop, crushed deliberately or from the weight of the ground over time.

A photograph of X rays of the curved iron bar find number 70438 taken of its side, from a top view and from the bottom, revealed its loop shape.

Image: Photograph of the new X-ray of find 70438.


All thirteen finds were deemed interesting and were added to the ‘interesting’ shortlist.


Unboxing (and Re-boxing): Prioritising Objects Part 2

It was unlikely we would make it through twenty-eight finds in addition to a practice object and the other projects we were working on during the four-week placement.

I narrowed the now-longlist down to sixteen objects. I chose the most aesthetically pleasing and rarest objects in the context of our collection. As well as yielding the most information about the site, these would be the most interesting to the public, who might, in the future, come to see the finds on display. I christened this the ‘super cut/high priority’ list.

To help us keep track of which objects had been treated and by who, Tessa made a table assigning students to in-progress and completed objects.

A table drawn on a whiteboard, titled 'Repton' and featuring a list of first names, the object numbers assigned to them, and ticks.

Image: Tessa’s table, assigning objects to the seven students on placement.
The ticks to the right of find numbers represent fully air-abraded and readhered (where necessary) objects.


However, this did not speed up finding the objects we were currently treating in a box containing 130 others. To increase our efficiency, I separated the ‘work in progress’, ‘high priority’ and ‘interesting’ finds into separate boxes, adding bags of silica gel to limit corrosion caused by introduction of moisture and oxygen from regular opening and resealing.


Treatment Stage 2: Air Abrasion

It seemed advisable for us as students relatively inexperienced in air abrasion to practise cleaning down to the magnetite layer on less ‘important’ objects with similar corrosion patterns to the more significant finds.

There are an enormous number of nails surviving from the eras of Roman, Saxon and Viking occupation. Therefore, anything identified as a nail was designated an acceptable practice piece.

A stubby nail with a broad head covered in lumpy grey-brown corrosion resting on a small plastic bag on top of the glass lid of an air abrasion cabinet.

Image: My air abrasion ‘practice’ object, a short iron nail, before cleaning.


A student with red hair in a plaited bun wearing a white lab coat, ear defenders and a face mask sits in front of an air abrasion cabinet. She looks through the glass panel on the upper face of the cabinet at the abrasive nozzle she is holding in gloved hands as she guides it over the surface of an iron object. Over-the-shoulder shot of a student wearing a white lab coat and a face mask looking through the glass panel of an air abrasion cabinet while she cleans an iron object by guiding the air abrasive nozzle over its surface.

Image: Courtney (top) and Emma (bottom) air abrading iron finds.

Only a few of the ‘high priority’ objects were cleaned completely while we were on placement. However, our work prepared the way for air abrasion to continue after the summer break.


The digs at Repton also uncovered several ‘special’ finds, made of more precious metals and/or thought to be especially beautiful examples of Viking metalwork. You can learn about their conservation here:


Further reading


Interested in finding out more about what conservators do? Check out:

Mathiasson, J. and Rumsey, K. The C Word: The Conservators’ Podcast [Podcast]. Available at:

Secrets of the Museum. 2020. BBC Two. Available at:


To find out more about how we use X-rays to interpret the condition and construction of metal objects:

Historic England. 2006. Guidelines on the X-radiography of archaeological metalwork. Swindon: English Heritage Publications. Available at:


You can find out more about our work on the Repton finds, and about our work at Cardiff as conservators, on our social media!















History and Archaeology

BBC. 2014. Viking Dig Reports. Available at:

Butler. J. n.d. The Great Heathen Army. Available at:

Current Archaeology. 2019. Resolving Repton: A Viking Great Army winter camp and beyond. Available at:

Hadley, D. and Richards, D. 2021. The Viking Great Army and the Making of England. London: Thames & Hudson.

Jarman, C. 2021. River Kings: A New History of the Vikings from Scandinavia to the Silk Roads. London: HarperCollins.

Levine, J. 2022. Digging Up the Rich Viking History of Britain. A massive 1,100-year-old graveyard leads to a surprising new view of the Nordic legacy in Britain. Available at:

Richards, J. 2021. The Viking Great Army: the latest discoveries. History Extra [Podcast]. 7 July 2021. Available at:

The British Museum. 2022. Portable Antiquities Scheme. Available at: – This scheme records archaeological objects discovered by the members of the public in England and Wales on a searchable database.

University of Nottingham. 2022. Vikings in the East Midlands. Available at:


All images belong to me or the other students who worked with me on the Repton finds, unless stated otherwise.