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17.10.2019

Joe G. Martin: "Conserving objects from Lincolnshire’s Anglo-Saxon heritage"

The discovery of several Anglo-Saxon artefacts in 2018 by a detectorist in Scremby, Lincolnshire, soon led to the uncovering of a large Anglo-Saxon cemetery (late 5th to mid 6th century A.D.). The site contained an array of artefacts from elephant ivory rings, decorated copper alloy brooches and silver buckles to iron spears and shields. Showing a large community and the lifestyles of those who once inhabited the area. The dig was also widely covered in the media; featuring in the BBC’s Digging for Britain.

Dr Hugh Willmott and Dr Katie Hemer, of the University of Sheffield’s Department of Archaeology led the dig, with the collaboration of Dr Adam Daubney, the Finds Liaison Officer for the Portable Antiquities Scheme, Lincolnshire. As a student of Conservation of Cultural Heritage at the University of Lincoln, my peers and I had the fantastic opportunity to conserve some of these finds, thanks to Adam Daubney’s relationship with our department. This was also a chance to examine a piece of Lincolnshire’s own heritage and learn about the people that once inhabited the land.

3_1.jpg

The iron spear socket before treatment

 

The Objects and investigative analysis:

The artefacts that I worked on consisted of three separate objects from different graves, these included:

An iron spear socket, which would have attached the spearhead to the wooden shaft.
A small copper lace fitting/ lace end; a decorative clothing accessory which stops the ends of clothing material from fraying.
An iron shield boss which would have been mounted to the front of a wooden shield with rivets; providing distance and deflecting enemy blows when used in combat. 

Although the spear socket and shield boss were both iron weapons, the different investigation, cleaning methods and consolidation required for each object meant that a varied approach to treatment was required and tested my skills between method.

The artefacts had evidently spent an extended period of time in burial, becoming heavily corroded and encased in dirt. This reduced visibility of the surface, and a condition evaluation was completed in order to assess the level of damage and to prevent exacerbating the objects condition during cleaning.

This was primarily achieved through X-ray analysis of each object in order to discover any major damage under the soil that could not be seen through visual examination alone. The copper lace fitting for instance; had a large structural crack running down the side, along with  active corrosion, the removal of tough dirt with mechanical cleaning may have applied excessive pressure and damaged the thin, metal object.

The X-ray images provided significant information when investigating the shield boss. The hollow, bowl-like object contained a collection of broken pieces of the rim of the shield boss, as well as original wood from the shield, human bone fragments and an iron shield handle. This could not be seen before cleaning and helped to plot the location of material inside of the shield boss during micro-excavation of its dirt-compacted inside. This was also a vital source of recording as the X-ray created a depiction of the material in-situ before removal.

The early stages of investigation was also a chance to explore the use of XRF (X-ray fluorescence) analysis. A small rivet with a slightly shiny corner accompanied the shield boss; research suggested that these were occasionally forged from a copper alloy, XRF analysis on the rivet concluded that it was simply iron and the appearance was a product of blistering from oxidation.

1_0.jpgThe copper lace fitting with active corrosion

 

Treatment:

The approach to these objects was to remove the heavy surface dirt and consolidate the artefacts in order to preserve them for display. This was achieved through techniques that would remove the dirt without damaging the surface, whilst investigating the different elements of the objects during the cleaning stage. For example: whilst removing soil from inside of the spear socket, I remained conscious to the fact that some original organic material may have still been present, removing soil using a toothpick under (60X) magnification.

The removal of internal soil from the shield boss was achieved through micro-excavating the dirt 1mm at a time. Each layer of soil would be swept away using a small and soft brush, so as not to damage any fragments of wood or human bone. The presence of human bone, most likely rib due to position on the chest during burial, was first identified using UV light. This enabled highlighting and plotting of the fragments (with photography). Images were also taken for each layer that was removed in order to document the material in situ.

Due to the fact that both the remaining original wood and bone were loose in the dirt, the only viable decision was to document, remove and collect the fragments during the cleaning. It was essential to remove all of the soil (approx. 600g) as this extra weight posed a risk to the object during transportation as well as holding moisture, and causing continued corrosion of the iron shield boss.

Air-abrasive with aluminium oxide was an essential tool for cleaning the iron objects, this method meant that layers of uneven corrosion could be removed and focused on, without the pressure that comes with hand tools such as dental picks. This method was only utilized on masses of corrosion present on the shield boss and spear socket. The copper lace fitting/ lace end was cleaned, using a wetting agent with a small cotton swab under magnification. A vacuum chamber with a bath of benzotriazole was then used for inhibiting copper corrosion before application of Incralac.

After cleaning each object, the final step was to apply protective coatings. Coatings do not always function well however this was vital in the preservation of these objects, protecting them to some extent from the surrounding environment (relative humidity) This also helped to stabilize the objects by giving strength to the fragile surfaces. ParaloidÔ (B72 and B48N) were used for this by applying a thin coating to each object.

This was an incredibly interesting project conserving the different selection of objects over the last year. Working on these artefacts was a chance to apply newly learned skills in archaeological conservation techniques; whilst developing those in decision making and using the various analytical methods that the university has to offer. Hopefully the future will contain many more interesting artefacts waiting to be worked on.

5.pngThe iron shield boss (pictured in header) after treatment

 

Acknowledgments:

The artefacts were provided by Dr Adam Daubney, Dr Lisa Brundle and the Portable Antiquities scheme in Lincolnshire, I am very grateful for the chance to work on them.

Archaeological wood expert Mike Bamforth helped me greatly with identifying the wood fragments of the shield boss, many thanks for taking the time to look at the images and providing me with source material.

The conservation techniques, knowledge and use of equipment were provided to me by the fantastic lecturers and talented lab technicians at The University of Lincoln, department of Conservation of Cultural Heritage, thank you all.

 

All images: © Joe Martin


Do you have your own story to tell? Let me know at cinesta@icon.org.uk!

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