X-ray

CSI: Sittingbourne Volunteers & Their Tools

Adapting ‘pin vices’:

Janine and I discussed her progress on investigative conservation of one of the Grave 111 shield studs She has brought in thorns from her garden to use for careful cleaning of the soil and corrosion around the shaft of the stud – this area has mineral preserved wood, reflecting the shield board itself. We got the idea of using thorns after watching conservation work on the Staffordshire Hoard.  Janine feels more comfortable with the softness of her thorn pin vice.

Janice was working in the afternoon on a spearhead from Grave 111, she prefers to use a very fine needle pin tool, that she made herself and brings with her for her sessions, when she is working on an object with fragile or intricate details (eg. mineral preserved textiles).

 

A volunteer’s tool and X-ray of spearhead from Grave 111

CSI conservation volunteer Janine working on a shield stud from Grave 111

 

 

A day in ceramics, glass and metals. Conservation at the British Museum

8.55 am. Misting a waterlogged leather purse inside a pot with deionised water.

The purse contained a hoard of silver Civil War coins currently going through the Treasure process. If the leather dries out, it will distort. Treatment is delayed while questions of ownership and ultimate destination for the hoard are resolved but we have pressed for a speedy decision!

9.05 am. Excavating fragments of an Iron Age cauldron from a soil block.

This is just one of a group of bronze cauldrons, some with iron rims and handles, found at Chiseldon.

9:15 am: Identifying old restoration on a bronze portrait head of Augustus under ultra violet light.

The results of the investigation will be published and the head may go on display. You can find out more about the head of Augustus on the British Museum website.

9.22 am Revealing silver inlay in an iron Merovingian axe wanted for The World of Sutton Hoo exhibition that will open in September 2011.

Further details on the handaxe can be found in collections online.

9:30 am: Two 18 month contract posts have just started to clean coins from the Frome hoard, the largest hoard of Roman coins in a single pot found in Britain. They have calculated that they will have to clean about 40 coins each a day to fulfil their contracts.

An extensive blog has been posted by the Portable Antiquities Scheme on the discovery of the Frome Hoard and it will form part of a video conferencing workshop for children.

9:32am: Piecing together fragments from the old Naukratis excavation.

You can read more about the Naukratis research projecton the British Museum research pages.

9:37 am: Reconstructing the bowl that was placed over the mouth of the pot that contained the Frome hoard.

9:54 am: Removing a tiny wisp of cotton wool caught in the gold cloisons of part of the Ostrogothic Domagnano Treasure.

You can learn more about this object on Collections online.

12:32 pm: Reconstructing the pot that contained the Frome Hoard.

12:40 pm: More joins found in the Naukratis material.

12:43 pm: Editing a conservation record on the British Museum computer system. Recently it was announced that the 2 millionth record had been generated and most of these are open to the public via the BM Collections On Line website.

1:58 pm: Consolidating lead items that have formed part of a comparative study of galvanostatic and potentiostatic methods of reduction.

2:23 pm: Still gluing the Naukratis fragments.

2:26 pm: Still building up fragments of the Frome pot. (Note picture on the wall of the pot still in the ground.)

2:59pm: Investigating the Lilleburge assemblage, a collection of Viking objects that includes items still in the small blocks of soil in which they were excavated in 1886 from a long barrow in Norway.

For more details on the Lilleberge assemblage, visit these pages.

3:01 pm: Filling gaps in the Frome bowl.

4:58 pm: Examining an X-ray of a cheek piece from the East Leicestershire helmet made from iron overlaid with silver gilt. The helmet, which dates from just before the Roman invasion of Britain, was part of what was originally called the Hallaton hoard and was buried full of Iron Age silver coins

The Hallaton hoard has been acquired by Leicestershire Museums Service and Helen Sharp blogs about the treasure elsewhere on this site.

5:23 pm: Removing tarnish from an Anglo-Saxon silver gilt buckle for The World of Sutton Hoo exhibition that will open in September 2011.

You can find more information on the buckle on the BM site.

Anglo-Saxon CSI: Sittingbourne (Conservation Science Investigations)

CSI Volunteer Richard Senior's raw gold and garnets

Investigative conservation of Anglo-Saxon grave goods

The X-raydiograph shows copper, iron and bone - decorations sewn onto a tunic perhaps?

Conservation volunteer Pat at the microscope

Today I have been supervising some of my volunteers and speaking to visitors at our shopping mall conservation lab. We have been running for nearly two years and have just reached 5,000 volunteer hours for investigative conservation of several hundred artefacts from 65 graves. We are on the last grave for this project – but there is still the finds from the other half of the cemetery to be worked on. Tomorrow we close our doors for fundraising for that project. fingers crossed that we’ll be open again soon! For general info on our community conservation project see a great video made on our opening day – http://digital.kent.gov.uk/2800. and/or visit our website – you can also ‘befriend’ us if you like as we just set up a facebook page too. Volunteer Pat Horne says: ” Today I am working on an object that is really perplexing. It is a ‘blocklifted’ assemblage of finds from a woman’s grave. I am trying to discern the different materials it is made from (we have found mineral preserved bone and textile, possibly leather iron and copper alloy). It has become very fragile, so I am repackaging it to make it more secure before continuing to work on it. this artefact has to be looked at along with others in this grave. There are several with the same ‘figure 8’ copper alloy shapes. so imagination is working overtime trying to puzzle it out – great stuff!” .

Janice Monday is also working on a find from a woman’s grave: “I am working on a small object which, from the X-ray, appears to be minute thin pieces of wire bundled through a loop possibly of bone. there are three more baffling pieces associated with the main part.”

Both Pat and Janice have been volunteering at CSI: Sittingbourne since we began in Oct. 2009 (2 and 1 days per week). We have recently begun training a new group of volunteers (there were 80 on our waiting list!) – one of our new recruits has just returned from panning for gold in Northern Scotland… he popped in to show me some of the gold and garnets he came back with. I didn’t know that garnets were sometimes found alongside gold, when panning – we decided we should look out what is known about the sources of gold and garnets in the Anglo-Saxon period and I encouraged Richard to join the Historical Metallurgy Society to find out more about those iron age camps located at his ‘gold hot spots’ that he was wondering about. We also discussed him posting up his photos to our facebook page and staying in contact while we are closed for fundraising.

– Another day draws to a close at CSI, now on to other tasks, like writing a reference for a past conservation student intern and submitting a paper for publication in the proceedings from PARIS4, Copenhagen… that’s about my conservation work on an early Christian monastery on Sir Bani Yas Island, Abu Dhabi, but that’s another story…


Ancient concrete? Really?

Yes, really.  I first fell in love with old buildings in Pompeii, where I spent summers working as an excavator from 2002-2008. Every day it struck me that I was in a place that still looked and felt like a real city. To my mind, this was down to the fact that the buildings are still standing. After more than 2000 years. Someone did something very, very right when making those buildings and I want to know more.

For my D.Phil research, I have landed in an opportunity to study structures in Ostia, Italy, which is also a preserved city-sized site.  The structures I’m investigating are all brick and mortar masonry, with concrete filling up the center wall core. This is what Vitruvius called opus caementicium. To be honest, I’m most interested in the people who made it: the builders who developed this wonderful, magical material that is still performing successfully more than 2000 years after it was first installed. Where did they get their materials? Why were certain materials preferred over others? How were the materials processed and mixed together? How did builders’ choices affect the concrete and its performance? Were the same mix types used for both public and private structures? Why is this stuff still standing? These are the questions driving my research, and I am looking to answer them by investigating the material itself.

To give a quick overview, the mortar and concrete I am analyzing was made of lime, volcanic sand aggregate, and water. Sounds rather simple, however, the combination of materials they were using produced complex chemical reactions, known to modern concrete scientists as pozzolanic reactions, which resulted in a sophisticated, high quality material. My sample collection was collected from a series of structures in Ostia from the 2nd century CE, by which time – at least in Rome – concrete was well-developed and had been employed in large-scale Imperial building projects. My task now is to analyze the Ostian structures to determine how well-developed their concrete industry had become by that time. The benefit of a site like Ostia is that the ancient city is left largely in tact without modern development. This means that unlike in Rome, where centuries of modern development has destroyed all but the most protected monumental structures, it will be possible to evaluate the buildings within their original cultural context.

The analytical techniques employed for my research are borrowed from geology and concrete science, which makes this a truly interdisciplinary project. My samples are essentially synthetic composites of natural materials that can be investigated with traditional petrography. I’m using light microscopy of thin sections to identify and quantify the aggregate, to describe the cementitious matrix, and to identify any  obvious degradation features or alteration products. Today I’m working on point counting one of the samples, which is pretty straight forward. I move across the sample in 1 mm steps, and at each location I record what I see in the cross hairs of the eyepiece. Besides the obvious benefit of quantifying each of the different components, I’m also getting to the know the sample really well. As I go, I’m recording information about the state of degradation or alteration, the shape and fillings of any cracks or holes, particle size and shape, and any other details that may give me a clue about what the builders were doing when they made the concrete.

I am also using scanning electron microscopy (SEM) to collect high-resolution, high-magnification backscatter images of the samples. At this scale I can get a better look at the binder-aggregate interface to see how well-bonded these components are. It is also possible to see any microscopic cements that have formed in pores, cracks, and the vesicles of aggregate clasts that would otherwise not be visible. The SEM also detects the atomic weights of everything in the sample, which show up as differences in the greyscale colour of the image. It  also can calculate the chemical composition of the different components, so using a combination of chemical data and backscatter images, I can determine what types of cements have formed (strengthening) and how much leaching has occurred across the matrix (degradation). The ratio of calcium to silica is key in both cases.

X-ray diffraction is also on the menu, assuming I can find the funding to pay for it. This technique is incredibly useful for identifying the mineral assemblage in rocks and materials. In this case, I will use it to confirm the original petrographic identification of minerals in the aggregate and to find any other alteration minerals that could not be seen in thin section. The presence of certain minerals like gypsum or ettringite usually indicate alteration of the mortar itself, but minerals such as stratlingite and calcium-aluminum-silicate-hydrates suggest the mortar was rather well-formed in the first place.

So today, I’ll be giving an account of what it’s like for me in the lab. I realize that being stuck in the lab sounds like a death sentence to some people, but for me, it’s where the magic happens.