A Stony Situation

With a very busy summer coming to an end, you might expect life at the Roman Baths to quieten down a little - but things couldn’t be further from the truth! The Archway Project is in full swing, with some preliminary excavations in the vault beneath York Street in central Bath already unearthing some exciting surprises.

Archaeologists at work in the York Street vault

When the Archway building works under York Street are completed and the new Investigation Zone is opened to the public, it will be filled with Roman stones from the site as part of the interpretation and display. The Collections team and our volunteers have undertaken the laborious task of recording hundreds of stones, some previously unidentified and many untouched since their discovery by the Victorians.

Identifying stones at our offsite store 

With all hands on deck and a crack team from Cliveden Conservation, who lifted, weighed and sometimes turned each stone individually, we recorded 202 stones with weights going up to 620kg in just 10 days!

Cliveden Conservation lifting and weighing a stone from the Roman Baths

In that time, Cotswold Archaeology joined us for three days to create a 3D photogrammetric record of 15 specific stones. This involved taking hundreds of photographs of each stone from every angle possible in order to create a digital 3D model that can be examined in minute detail, rotated and moved around with ease on a screen. The chosen stones will be used in an app for schoolchildren to identify specific types of Roman building blocks and manipulate them on screen, learning more about Roman building and how the Roman Baths may once have looked.

Photogrammetry in action!

The results of this work will also be incredibly helpful as a conservation record for our collection, showing the stones in a way that allows us to easily examine, compare and move them around without having to physically lift these huge blocks again! Our plan is to produce a 3D model of every stone that we have been examining, and with this technology at our fingertips continue to learn more about our incredible site for years to come!

A sea of stones, recorded, weighed and identified

For more information about the Archway Project go to our website and keep an eye on our Facebook page for updates as they happen!


Zofia
Collections Assistant

Saltford Festival: Musings on Metalwork

Roman Baths object handling at Saltford Brass Mill

At the beginning of June, our Collections and Learning teams packed up the van and spent the day at Saltford Brass mill for the Saltford Festival.

We took a selection of archaeological metalwork to fit with the theme of the location, choosing objects from the local area and that could showcase the use and preservation of different types of metal.

Copper Alloy

A pair of Roman tweezers found in Keynsham

As we were in a Brass mill, brass would be the most fitting metal to choose! However, archaeologists choose not to distinguish between brass and bronze, instead using the term ‘copper alloy’. Bronze is a mixture of copper and tin and brass is a mixture of copper and zinc, and without scientific testing it’s very difficult to distinguish between the two.

You can recognise copper alloy from the tell-tale green colour caused by corrosion, sometimes called verdigris.

Iron

A selection of iron objects including an axehead from the site of the Thermae Spa in Bath

Again, iron is recognisable from the way it corrodes, producing distinctive red rust. As with all metals we do our best to slow down and prevent this process, keeping the objects as dry as possible in sealed containers with packets of silica gel to absorb any moisture.

The objects pictured are in particularly good condition. Archaeological metalwork is not always so lucky!

Lead

A piece of the lead sheets used to line the Great Bath

Lead from the Roman Baths has survived incredibly well and some Roman pieces are still in place, for example the sheets that line the Great Bath. We took a section of that lead with us to Saltford, and almost everyone commented on the incredible weight of just this one small piece!

You may question the use of lead, and rightly so. Today we know that it is poisonous, and we definitely wouldn’t use it to line our baths! However, the Romans didn’t know this and instead prized it as the perfect material for plumbing.

Silver

A silver coin of Julian II

There are a number of silver objects in the Roman Baths collection, and most of them are coins. The examples we took to Saltford included a Roman Imperial coin known as a siliqua of Julian II, made at the mint at Trier, Germany. 

Silver is a perfect choice for making currency, and even though this coin is well over 1,000 years old the design is as crisp as the day it was struck! 

Did you know?

The Latin for Lead is plumbum (also used for its chemical element symbol Pb), which is where the word ‘plumbing’ comes from!

Zofia

Collections Assistant

Spiders invade St John’s Store

As part of our Heritage Open Week event at our St John’s local history store this year we had a trail looking at our pest management procedures, – not as dire as it sounds!

We positioned large dangling plastic spiders as clues to the location of pictures of pests and their food stuffs. Children had to connect the pest with what it eats and how we stop them from damaging our collection.

So for instance, one spider sat above our bath chair, and on its fabric lined seat was a picture of a clothes moth and a moth trap was placed nearby.  This fiendish device contains pheromones which attract then trap male moths so they can’t go and find females to mate with… 

Insect traps are in the forefront of our battle against the creepy crawlies: silverfish eat paper so visitor books, letters and posters are at risk, but as a non-flier it is easier to control. However, the inappropriately named woodworm, actually a beetle, are the greatest threat in St John’s with 39 pieces of furniture stored there. Again insect traps near windows and doors help.  Regular visual checks ensure none get their teeth into the wood.  If furniture is infested, treating with a special insecticide and then keeping them isolated from the rest of the store, ensures no beetle escapes.

The handy English Heritage guide to Museum pests

The number of nasty nibblers who love wool, carpets, and other fabrics are many.  But they were represented in our quiz by the carpet beetle, again caught by insect traps and vigilant checking. 

Rodents are always a concern in old buildings and St John’s is in an 1875 school, but, mercifully, all holes are blocked and we do not suffer.   But traps and poison are used in the other buildings where we also store collections.

Children seemed to be unfazed by the prospect of killing pests and were very matter of fact about the demise of mice at home.

Good housekeeping: regular checks and cleaning are important and when not open, we use Tyvek covers to protect the collection. And at the event we displayed these and some of the tools we use: from soft brushes, cotton buds, a hoover as well as protection for us, the cleaners: dust masks and vitrile gloves. 

Verity covering up the furniture in St John's after our event with Tyvek covers

The final question on the trail was whether spiders and humans were pests or friends.  Our young visitors quickly grasped the idea that although spiders catch flies, their webs make cleaning difficult and the sticky fingers and messy habits of humans are sometimes worse than the smaller pests!

Note: no pest (regretfully) was harmed during this event.

Susan

Ongoing Conservation

One of the more unique parts of my role at the Roman Baths involves the conservation of the monument. As you go around areas of the monument you will see the natural wear and tear of a site such as ours, nearly 2000 years old, and still being walked on by 100, 000s of people a year.

In order to preserve the monument we carry out a programme of work to stabilise of the monument that may be more fragile than others.

Around the walls of the Great Bath, you will see substantial areas of surviving Roman wall plaster; what you may not have noticed is that below this plaster (and sometimes about it), there is often a line of mortar, which differs slightly in colour and make up.

Spraying newly mortared wall to ensure it sets

 This line of mortar is known as sacrificial mortar. We apply it next to the Roman plaster to provide a barrier for the Roman remains, taking moisture away from it and supporting and preserving the Roman layers, more substantially than if we were to leave it unprotected against the elements.

We use the same types of ingredients for our mortar as the Romans would have done; lime, brick and sand, but the composition we use differs. If you look closely at the surviving plaster, you will see mortars with quite large chips of brick in, this tends to indicate that it is original Roman mortar (we use smaller brick chips in our modern mixes). We mix our modern mortars, to look similar to the Roman, but distinct enough that it can be seen where, the original lies and where the sacrificial mortar has been added.

Modern mortar below existing Roman plaster

Last month, I was down by the Great Bath, replacing some of the sacrificial mortar which had fallen away. The mix I used complements the Roman mortar nicely, not being too different so as to stand out, but still making it easy to spot where the Roman mortar ends, and my additions begin.

Verity

Winter Work at the Baths

After the busy Summer and Autumn months, the winter period is when we take the opportunity, as the site is quieter, to do maintenance and development work.

Visitors to the Roman Baths may have noticed that this year, that work seems particularly extensive. Just this week alone has seen scaffolding go up round the exterior of the Pump Room and across the Sacred Spring, in advance of work being done to repair the roof of the Pump Room, and to clean its exterior, and later in the month we’ll see scaffolding going up in the Great Bath for further improvements to the site.

Scaffolding erected ahead of repairs to Pump Room roof

 

However, the most extensive work is that going on behind the hoarding in the museum area…

The temple precinct area is currently closed to visitors as we are undergoing major development work to install a new walkway. This involves a substantial amount of work by contractors, including the protection of the monument before work began.

Temple Precinct protected against dust and damage during development work

Changes to the modern elements of the precinct, is uncovering some interesting features, including Georgian and Victorian elements of the building that had previously been covered up by false walls.

Victorian tiles and doorway in Temple precinct

The conservation of the site is an on-going feature of life at the Roman Baths, and we are constantly checking the environment on the site, and any changes to it. One event we are currently monitoring is the recent rise in water levels at the Roman Baths (and across the whole region!). Though they have now dropped down to normal levels, Christmas Eve saw us presented with some of the highest water levels on site staff could remember!

Water levels reached a significant height on Christmas Eve!

Keep an eye out for my next blog, about the more common conservation work we carry out on site…

Verity

Cold Conservation and Consolidation

Winter conservation signage

It’s been a while now since I took on the challenge of resetting the secondary Roman paving on-site. Since starting the task I have managed to reset quite a few pieces around the Great Bath although things halted over the winter due to the cold climate. Did you know that it recommended that you only use a lime based mortar between the months of April to November otherwise it won’t set properly? The Romans did…..

‘Repairs to be carried out without interrupting the flow of water are primarily those involving the use of concrete, work with which should be done in appropriate seasons and the product should be of durable quality. The suitable time for working with concrete is from the 1st of April to the 1st of November; but it is best, nonetheless, to leave off temporarily during the hottest part of summer, because moderate weather is needed for adequate absorbency of moisture and for cohesive solidity (intense sunlight causes premature setting no less than does frost). No material requires closer attention than that which is required to withstand the action of water; a reliable quality must therefore be demanded in such work, in accord with the rule which all know but few observe.’

(Sextus Iulius Frontinus - On The Water Management of The City Of Rome 123)

If you want to learn more about conservation here on site why not take a look at some of our previous blogs on the topic (links listed below)

Lime

http://bathsbloggers.blogspot.co.uk/2012/03/its-all-about-lime.html
http://bathsbloggers.blogspot.com/2011/05/its-all-in-mix.html

Objects

http://bathsbloggers.blogspot.co.uk/2012/01/conservation-consternation.html
http://bathsbloggers.blogspot.co.uk/2011/12/how-to-let-your-objects-know-you-care.html

Monument

http://bathsbloggers.blogspot.co.uk/2011/03/monument-in-mist.html

Helen Harman - Collection Assistant

It's all about... Lime

This week is National Science and Engineering Week at the Roman Baths and I have been charged with donning my other hat and talking to you all about Lime (not the little green citrus fruit)…..

So what is Lime?
Lime is a general term given to a number of compounds containing Calcium. This blog will be focusing on Quicklime and Slaked Lime. Quicklime is a white caustic alkaline substance consisting of Calcium Oxide, which is obtained by heating Limestone (Calcium Carbonate). Slaked Lime is a white alkaline substance consisting of Calcium Hydroxide, made by adding water to Quicklime and it is this form that is predominantly used in traditional building methods to make plaster, mortar and limewash.

Calcium Oxide Molecule

The diagram below shows clearly how Limestone or Chalk - Calcium Carbonate - turns into Quicklime (Calcium Oxide) after burning or heating. If water is then added it turns into Hydrated Lime or Slaked Lime (Calcium Hydroxide). The cycle is complete when it reacts with Carbon Dioxide from the air around it, turning it back into Limestone. This process is known as the Lime Cycle.

The Lime Cycle

So why is Lime so important in historic conservation?
Buildings pre 1900 would not have been built with modern cement (with few exceptions in the late 19th century), but with a lime mortar. In order to conserve and repair these buildings, it is essential to use similar materials such as lime mortars, lime plasters and renders.

Does it have to be Lime?
Modern buildings generally rely on an outer layer to prevent moisture penetrating the walls, whereas buildings constructed before 1900 generally rely on allowing the moisture, which has been absorbed by the fabric, to evaporate from the surface. In essence, old buildings exposed to the elements are continually absorbing moisture, and the ability for the moisture to evaporate again is crucial to the welfare of the structure. Lime based building material is perfect for this two way exchange.

Using modern cement based mortars and plasters in traditional buildings risks locking-in the moisture, which could result in dampness internally and spalling of brick and block externally, as a result of freeze and thaw.

Pop along to the Roman Baths today, Wednesday 14th March 2012 between 4pm and 8pm and see me in action. I will be on hand to answer any of your lime based queries and demonstrating how we use lime based building material on-site.

For more specific information on applied lime based building material here at the Roman Baths, take a look at my previous blog – It’s all in the mix.

http://bathsbloggers.blogspot.com/2011/05/its-all-in-mix.html

Helen Harman - Collections Assistant

Conservation Consternation

There are often times when I wonder how some archaeological finds have managed to hold together for thousands of years. I find this thought particularly alarming when handling metal objects – they are so easily damaged by long periods of time in damp or waterlogged conditions.

A Saxon Spearhead from Batheaston Bypass, still in one piece and stable.

Even metal objects found in good condition are threatened by corrosion, and all objects sometimes require specific care and treatment by experts. For example, the pewter vessels and other artefacts from the King’s Bath corridor are soon to be redisplayed, and have been sent out in groups for conservation. The objects were conserved when they were found, but over time, the state of their treatment and attitudes towards care has changed. The pewter objects in particular looked dull and were coated in a waxy substance that seemed only to attract dust. When the items were returned from conservation, the difference was amazing.

Pewter patera after conservation

It turns out that the majority of the work done was to remove the waxy coating and degrease the surface of each object. The coating was replaced with a fine layer of microcrystalline wax to provide protection, and buffed to shine. In a few cases, fragments were reattached and broken areas were filled. However, it seems that when considering conservation, less is without doubt more – the purpose is to protect an artefact without changing its composition or encouraging degradation.

Learning about different types of metals, surface treatments and the process of corrosion is very useful, if only to highlight how much could go wrong with metal objects! A major problem is corrosion, caused when a metal object combines or reacts with other elements to form an undesirable compound, such as tarnish or rust. Corrosion is different from patination, which is generally more benign and will slow and stop without intervention – this occurrence can be seen on copper clad roofs as a blue green compound known as verdigris.

Statue of Liberty – the blue green colour is a result of natural patination

Corrosion generally occurs preferentially, which means that it will affect a reactive metal in preference to a more noble metal. This is the primary reason for galvanising iron with a coating of zinc, which is preferentially eroded to protect the main iron sheet. The process of corrosion can only happen with the presence of moisture, so all metal is stored at a very low humidity. The corrosion of iron, even if contaminated, will not take place if the relative humidity of the surrounding atmosphere is 20% or less. For archaeological iron, such as the spearhead, a relative humidity of 18% or less would be safest, preventing any possible further deterioration.

If you’re looking to find out more about the scientific side to archaeology, National Science and Engineering Week at the Roman Baths, 9th-18th March 2012, is definitely a date for your diary!



Useful links:

http://cci-icc.gc.ca/crc/articles/metals/corrosion-eng.pdf  

http://www.collectionslink.org.uk/media/com_form2content/documents/c1/a130/f6/003024.pdf