Festival of Archaeology 2017

Conservation of Artefacts from the wreck of the London

I am pleased to welcome this month’s guest blogger Eric Nordgren of Historic England, who tells us more about conservation of artefacts excavated from a maritime context.

Eric at work in the lab
Eric at work in the lab. © Historic England

 

I have been working with Historic England as a conservation project assistant since November 2016. My main role is to carry out remedial and investigative conservation on artefacts lifted from the London protected wreck. The London was a Royal Navy warship that sank in the Thames Estuary following an explosion in 1665. A program of work to better understand this protected shipwreck has been under way since 2014, resulting in surface recovery of exposed objects and in two seasons of underwater excavation and recovery of hundreds of artefacts made of wood, leather, rope, ceramic, glass, iron, copper and lead. The London: Excavation of material at risk project is a collaboration between Historic England, the protected wreck licensee, Cotswold Archaeology, and Southend Museum Services, where the artefacts and site archive will be deposited.

The process of conserving marine archaeological material can often involve quite a bit of time and repetition: consider that 150 Apostle musket cartridge bottles have been recovered from the London, from complete examples with cap, to some that consist of just a few broken fragments. Each one has to be photographed, assessed, repackaged in soft nylon netting, wet cleaned to remove mud from the sea bottom, desalinated, treated with polyethylene glycol and freeze dried. I’ve just finished the wet cleaning stage which took 4 workdays!

At top of image, label naming the artefact with text '6901: The London 3527: wood'. Centre of image, wooden bottle, with stopper to left, body of bottle to right, underneath this is a scale marked off in centimetres.
‘Apostle’ musket cartridge bottles. © Historic England
Jumble of black bottles, all with individually numbered white labels.
Some of the 150 bottles after wet cleaning. © Historic England

It’s not just the Apostle cartridges, all the artefacts from the London have to go through similar stages.  The water in all 158 boxes of artefacts has to be changed every month in order to remove salt from the marine environment in a process called desalination. Both organic (wood, leather) and inorganic (ceramics, glass, metal) materials can be damaged if allowed to dry out while they still contain soluble salts such as sodium chloride. Artefacts are soaked in baths of distilled water which allows salts to diffuse out, allowing them to be safely dried. Desalination isn’t difficult, but it does take some time and requires knowledge of the drying behaviour of a wide variety of materials.

Though some stages of marine conservation are repetitive, there are lots of interesting moments as well. One of the most exciting things about archaeological conservation is finding out more about the artefacts during the process and especially discovering clues about who made them and the technology they used. This process is called ‘investigative conservation’ and uses a variety of tools and techniques such as microscopy, X-radiography and digital imaging.

Here is one example discovered during digital x-radiography of a pewter spoon:

Bowl of a spoon, darkened with age and contact with water, against a plain grey background.
Pewter spoon from the wreck of the London. © Historic England
Spoon seen in x ray as white against a black background, with red ring around the letters BA on the spoon. At top of image above the spoon is the Historic England logo.
Digital x-ray of the same pewter spoon from the London. Computed radiography revealed a touchmark of the letters ‘B A’. © Historic England

 

The letters ‘BA’ can be seen in the x-ray, just above the point where the handle meets the bowl of the spoon. Marks in this area are called ‘touch marks’ and can tell us where and when the spoon was made and who made it. Some marks on pewter made in London or Edinburgh can be identified by records on ‘touch plates’ kept by the Worshipful Company of Pewterers, but marks from the period of the London are difficult as many records from the Pewterers were destroyed in the Great Fire of London in 1666, just a year after the ship sank.  Still, it may be possible to identify who made the spoon based on comparison with other examples. We are hoping to find out more about who ‘BA’ refers to.

Another type of mark was found on a leather strap during wet cleaning. A stamped letter (or letters) can be seen in this photo taken with raking light illumination:

Horizontal strip of dark leather against a white background. Just off-centre to the right of the strip is a stamped mark resembling a letter P.
Leather strap from the London, showing stamped mark. Could it be from the leather worker or the artefact’s owner? © Historic England

Markings like this can be added by the leatherworker who made the strap, or might indicate its function or the sailor who used it on board the ship. We will pass this information on to the experts studying leather artefacts from the London.

Sometimes we find unknown or unexpected materials on artefacts during conservation, and need to investigate them further to get a better idea of what they are made of and why they are there. I noticed a yellow material with a tar-like odour inside the layers of a leather shoe from the London. Using a technique called Fourier-Transform Infra-Red spectroscopy (FT-IR for short) I was able to determine that it was indeed an organic material with chemical bonding similar to natural resins. This material may have been applied during the shoe’s construction as an adhesive or a sealant.

Two shoe soles one below the other, against a white background, and a centimetre scale rule underneath. Annotated on the lower sole where unknown tar-like materials have been seen.
leather shoe fragment from the London, with location of unknown material. © Historic England
Graph marked in units of 5 from 50 to 98 on the vertical axis, and 4000 backwards to 650 on the lower axis, showing significant spike between the 3000 to 2000 mark.
Transmittance spectrum produced during FT-IR analysis of the shoe sole. © Historic England.

Conservation work on material from the London is quite rewarding as we have a chance to progress artefacts from post excavation though conservation treatment, learning more through investigative conservation along the way and preparing them for storage and display at Southend Museum.

Find out more about the London by following #LondonWreck1665

Many thanks to Eric for his fascinating blog. The thing that caught my attention particularly was the stamped leather – that such detail has survived 350 years of immersion in a hostile environment and can be recovered by archaeology is amazing.

For more on conservation of artefacts from the wreck of the London, please also have a look at an earlier post from 2015.

 

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