Ever wondered what happens inside Historic England’s science laboratories at Fort Cumberland? Last week I was lucky enough to find out!
Down in Portsmouth at the very tip of Southsea seafront is Fort Cumberland, a pentagonal artillery fort erected to protect the Royal Navy Dockyard at Langstone Harbour. Built between 1785 and 1812, Fort Cumberland is now a Grade II* listed building where Historic England’s archaeologists and science labs are based. Each of the fort’s outbuildings is a different department, including Conservation & Material Science labs, Archives, Stores, Laying-Out Rooms and Finds Processing Labs. The Nautical Archaeology Society also rent space for their offices there too.
In the labs, Archaeological Conservator Angela Middleton is working hard to conserve objects from the London wreck, some big and some very small, which travelled to Fort Cumberland after their excavation back in 2014-6. Ahead of the London exhibition opening in September at Southend Museum, I spent a week at the fort to work with the objects and Angela, helping out with conservation, to get everything ready for the grand opening.
Archaeological investigation doesn’t finish at the end of an excavation, it continues well afterwards in what is known as the ‘post-excavation’ phase. At this time, researchers have access to the finds and work out what they are, what they’re made of and when they date from. I encountered one of these important questions on Day 1 when I worked with materials scientist Florian. He uses an X-Ray Fluorescence machine to assess the elemental composition of an object. Florian places an object from the shipwreck into the machine and x-rays are fired at it. The process works as follows: In the machine X-rays are fired at the object. These interact with the electron of the matter and produce “secondary x-rays”. These are analysed in a detector for their energy. Every single chemical element in the object produces x-ray of a known, specific energy. After a few minutes, a graph is produced with peaks at different intervals which correspond to different chemical elements. Florian had been analysing the metal navigation instruments from the wreck when I joined him. We chose to analyse some suspected gilding on a leather book cover. With baited breath we waited as the cover disappeared inside the machine and could barely contain our excitement when it was confirmed to be of gold! Cue social media frenzy…
One of the major processes involved when preparing marine artefacts for conservation is desalination. This is defined as reducing the salt content of the water that objects are being stored in. Using a sensor, I recorded the current conductivity of the water then changed it for a fresh supply of distilled water from the still. Over time the salt level in the containers reduces and the objects are deemed stable enough for the next stage.
For organic objects the next step was immersion in PEG solutions. PEG stands for Polyethylene Glycol. After a long time submerged in water, bacterial action causes cell walls in wood to break down making the wood porous and fragile. The spaces fill with water which keeps the wood in shape, but with removal of water, the wood would completely deteriorate. Waterlogged wood and other organic materials like leather are submerged in PEG solutions. The waxy PEG permeates the wood and bulks it up, keeping the wood stable. Leather objects only require 2-4 weeks in solution where some large wooden pieces need months. After this process, objects can be freeze-dried then any remaining PEG is gently brushed away.
All objects from the wreck required cleaning of some kind. Some wooden pieces had concretions on them (lumps of mud and stone) after a long time on the seabed. Using an airscribe tool (metal vibrating pen device) the concretions could be gently vibrated off and washed away. Other more delicate objects can be cleaned with an airbrush and water.
Throughout the week I also helped with conservation photography. In any archaeological excavation, photography is essential to document all the processes involved and the state of objects before and after conservation to see how their conditions change. Pre- and post-conservation photos get taken at the same angle and with the same scale, which makes it easy to compare the objects when wet and when conserved. It was fascinating to see the changes that the objects had undergone.
The London shipwreck project has been enormous, involving efforts from so many different organisations and individuals. It is now my job, along with Southend Museums’ curatorial team, to interpret the collection for the public in and exciting and immersive exhibition.
‘The London’ exhibition opens at Central Museum on the 22nd September and runs until July 2019.
Ellie Broad – Assistant Curator Archaeology