Mobilised Salts and Chedworth Roman Villa

Emma Prideaux

Anna has previously talked us through archaeological sites and how conservators assess them, using Billingsgate Archaeological site as an example. But what next? How do you solve a problem like sites next to a marina? Or with a water table that is jusssst a little too high? UCL’s work at Chedworth Roman Villa is a nice example of seasonal conservation work that tackles two problems caused by water: salt damage and microbiological growth.

The Villa

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The Villa Layout

Built in the 4th Century BC, Chedworth Roman Villa is one of the largest Roman Villas discovered in Britain. The significant remains of three wings (or ranges) of the building survive above ground, the best preserved of which contain the dining rooms and the bathhouses. Originally discovered and excavated in the Victorian Period, the villa is now managed by the National Trust. It is famous, amongst other things, for having the only depiction of a British Native in mosaic form.

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The mosaic shows a Roman-Era Briton. He symbolises winter, proving that the British obsession with the weather is really, really old. [http://quibono.weebly.com/]

While the site is stable and well cared for, the site is subject to problems associated with water movement. A relatively high water-table and run-off from the surrounding hills is partially combated by a modern French drain. The water that weasels its way through this defence has a habit of soaking into the foundations. This then allows water to spread to the other surfaces of the building, such as the mosaics. If this water dries, it leaves behind salts on these surfaces. If it doesn’t, it allows microbiological growth, namely algae, lichen, and cyanobacteria (think black sludge) to grow. This can damage and obscure the surfaces. UCL conservation students perform seasonal conservation work, removing salt and algae blooms to help National Trust staff maintain the site.

Cleaning

Sometimes, the cleaning of archaeological sites can involve delicate, painstaking work using specialised tools. Sometimes, as when removing efforvesence (salt blooms) from the surfaces of Chedworth Roman Villa, you do not.

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It’s too late for regret, Rob. We arrived in a communal van and there’s no public transport for you to escape in. You’re going to have to clean it.

It’s a simple process. Sponges are soaked in de-ionised water, which is then gently pressed against the surface of salt-encrusted tesserae. This dissolves the salt, and allows it to be lifted, wicking the encrustation away to reveal the surfaces underneath. By wearing thick socks, and laying down padded walkboards, we can move safely around the site.

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The cleaned tesserae!

Biological growth is slightly trickier. A fast way of killing and removing microbiological growth is through steam cleaning. These tools kill and remove the algae by applying high-heat steam to the organisms, where surfaces are stable enough to use it. You can see the progress and, as we’re essentially ‘boiling’ the algae off, you can also smell the over-cooked cabbage aroma of progress.

However, some areas (such as the mosaics) are too unstable to use steam cleaning. If attempted, we risk dislodging the tesserae en-mass, and beginning the world’s most stressful jigsaw puzzle. Therefore, microbiological growth is removed slowly, using these very special conservation tools:

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Pictured: “Specialized tools”.

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Conservation may be a dorky profession, but we’re always prepared for a barbeque.

But using tiny tools on huge mosaics is time consuming – even by conservation standards, which is saying something. Therefore, in this site we’re borrowing a trick that aquarium-owners use to keep their fish tank clean.

No. Not like this. Chedworth isn't that damp.

No. Not like this. Chedworth isn’t that damp.

Many fish tanks use UV light to kill algae. By exposing the microbiological growth in Chedworth Roman Villa to specific UV light for four days, we can kill it. As we are able to completely killing the microbiological growth, this process will also slow down the rate that biological growth will colonise in this area. An added advantage is that it also vaporises the remains, leaving the mosaic surfaces largely clear of debris. Any residual remains can be cleaned off using toothbrushes and bamboo sticks much, much faster.

Like painting the Forth Bridge, in moving the UV light source from section to section, it takes some time for the whole surface of the mosaic floors to be treated. This means that the UV eradication takes place when Chedworth is open to visitors.   To protect visitors from the UV light, the equipment is contained inside a light proof box , which make it perfectly safe for people to be in the same room.

Having carried out these cleaning techniques, our field trip to Chedworth has left the site cleaner, more stable, more accessible, and more visually appealing. Although it is not possible to totally prevent microbiological growth and salt blooms on the site, these techniques can be used to mitigate the damage that might otherwise result, if left untreated.

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Olduvai Gorge Conservation Project

Anna Funke

This is a slightly different blog post from what we usually talk about. It is supposed to introduce you to a fascinating project that Abby, Jan and I (all MSc Conservation students who you have heard from in the past in previous blog posts) will be involved with this summer. Although our degree has archaeology in the title, you may have noticed that these posts very rarely talk about the adventurous excavations of lost civilisations in foreign lands.

Well that is about to change! The three of us, also known as the GTCT (Greatest Tanzania Conservation Team) will be going to Olduvai Gorge in – you guessed it – Tanzania this summer! We will be in pursuit of some hard-fast evidence about the lives of early man and woman. This famous site is right at the heart of the theory that humanity’s origins are to be found in East Africa.

Olduvai gorge map

The archaeological research at Olduvai focuses on the transition between the Oldowan and the Acheulean. Both these groups are steps in the line of the human biological as well as technical evolution. The archaeologists on site will therefore be looking both for human remains that can give some insight into the biological stages of our development, as well as for ancient stone tools that can shed some light on our early technical developments. The finds from Olduvai Gorge go back as far as 1.7 million years!

Our contribution to these grand questions will be to try to stabilise these fragile finds so that they can safely be studied. We will also try our hands at excavation by helping out with the lifting of particularly fragile finds.

A Tanzanian student in the Laetoli Lab working on a horn core. Photo courtesy of OGAP.

A Tanzanian student in the Laetoli Lab working on a horn core during last year’s excavation. Hopefully, this will be us soon! Photo courtesy of OGAP.

We are now in the final weeks of preparations before the departure of GTCT in early July! We are getting our vaccinations and gathering our tents, travel showers, and tool kits. We can’t wait to jump in and we hope you will stay tuned for updates during the excavation! If you would like us to send you a postcard, we will happily do so in return for a small contribution to our travel fund. We are so close to going but we still need to raise the last of our balance to make this trip a success! You can help by contributing here or by spreading the word about our project. Thank you for any help you can give!

Find out more about the conservation at Olduvai Gorge here.

We came, we saw, we will maybe conquer … one day.

Anna Funke

Billingsgate House and Bathhouse is one of the many archaeological sites hidden beneath the streets of central London. This remnant of Roman Britain can be found in the basement of a rather unassuming office complex on Lower Thames Street, between Monument and Tower Hill.

One of the best preserved parts of the Bath House showing the underground structure of the heating system, part of the original floor, as well as a bench.  Photo Credit: Valeria Cabrera

One of the best preserved parts of the Bath House showing the underground structure of the heating system, part of the original floor, as well as a bench.
Photo Credit: Valeria Cabrera

In the 3rd century, when this House was built, it would have been right on the banks of the River Thames, providing it not only with a beautiful setting, but also with easy access to fresh water for its bathhouse and other household necessities. However, what was a very convenient feature during its occupation, has become a complicated conservation challenge today.

Although the occupants of the London area have been changing the flow of the River for centuries, the ground water table remains high and our archaeological site, in turn, remains damp.

The current setting of this Roman dwelling probably used to be much more romantic!  Photo Credit: Kristen Gillette

The current setting of this Roman dwelling probably used to be much more romantic!
Photo Credit: Kristen Gillette

Water movement through the site brings with it a rich array of soluble salts. These travel through the remains of the Bath House, while they are dissolved in water, and crystallise whenever the environment gets drier (hence the term ‘soluble’ salts). These salts are slowly but surely causing a variety of damage, including delamination of the ceramic building materials and crumbling of the original mortar.

A particularly impressive bloom of salts. Photo Credit: Kristen Gillette

A particularly impressive bloom of salts.
Photo Credit: Kristen Gillette

One of many examples of delamination on ceramic tiles at Billingsgate. Delamination is the separation of layers of material fabric.  Photo Credit: Kristen Gillette

One of many examples of delamination on ceramic tiles at Billingsgate. Delamination is the separation of layers of material fabric.
Photo Credit: Kristen Gillette

This is a complex conservation problem to solve , given that there is a ready supply of dissolved salt in the ground water and that it is not possible to achieve environmental conditions that could minimise evaporation of the water and crystallisation of the salts. One response has been to add ‘sacrificial sand’ to areas of the site around the archaeological remains. This acts to encourage groundwater to move through the sand instead of the archaeological remains, and thus reduce salt efflorescence on the actual structure. In spite of this, the salts nevertheless continue to appear on the archaeological remains. Although the salts are certainly a conservation problem in the long run, they also damage the public perception of the site as they give the impression that the Bath House is unloved and not well cared for.

Contesting this impression, students taking the Applied Heritage Management Master Class at the Institute of Archaeology work on the site every year to improve its accessibility, interpretation and condition.

The 2015 Conservation Team from the left: Kristen Gillette, Anna Funke, and Valeria Cabrera. Photo Credit: Tim Williams

The 2015 Conservation Team from the left: Kristen Gillette, Anna Funke, and Valeria Cabrera.
Photo Credit: Tim Williams

The conservation part of this project this year focused on recording the distribution of salts and the damage they have caused. We mapped the general distribution of the salts, identified areas of damage on different materials and in different areas of the site, and also compared the concentration of this year’s salts with pictures taken during last year’s survey.

Our findings point to the need to increase the frequency of regular cleaning and removal of the salts. An annual cleaning would help reduce the presence of salts onsite, and mitigate future damage from the crystallisation of salts. This would be good for the long term stability of the Bath House, but would not remove the cause of damage, as ground water continues to move through the site, depositing the damaging salts. Improving the care of the Bath House will make it more interesting and enjoyable for visitors, and this may bring about better opportunities for funding for the long-term preservation of the Billingsgate Bath House. This is just one of many examples when conservation and public engagement work towards the same goal of making heritage more accessible to a wider audience, both for the benefit of the archaeology and the people interested in visiting or researching it.