Articles tagged with: CMAS

X-radiography in the conservation lab

on Monday, 16 March 2020. Posted in Conservation, History Centre

X-radiography in the conservation lab

I have been working as a Conservation Assistant at the WSHC for nearly a year, and a large part of my role involves administration and financial processing. However, one of the more interesting and slightly unusual aspects of the job is the hands-on work I get to do as part of the Conservation and Museums Advisory Service here at the centre, and I have recently undertaken training to use the x-ray machine which we have in the lab. This is a complex process which requires stringent processes, records and maintenance checks to ensure the machine is used safely and functioning correctly. Regular use of the equipment is key to building experience and a ‘feel’ for the items being investigated and how to get the strongest images.

How it works

Inside the x-ray machine is an x-ray tube. A heated filament called a cathode sits inside the tube and accelerates high energy electrons at a metal target anode, usually made of tungsten, as the electrons strike the anode they interact with the atoms. In this process, which is called Bremsstrahlung (braking radiation), the electrons lose much of their energy and a photon x-ray is produced. X-rays are electromagnetic radiation of a short wavelength and high frequency invisible to the human eye, but possible to record on photosensitive film, known as x-radiographs.

Left: X-ray machine Right: Objects placed on a cassette in the middle of x-ray machine

The object to be x-rayed is placed on top of a cassette which holds the photosensitive film. On exposure the x-rays will penetrate through the object leaving the image captured on the film. The x-rays are partially absorbed, “attenuated”, by the denser materials such as bone or metal and pass more easily through soft material such as soil or skin. Therefore, the strength of the x-ray (KV) and the length of time the object is exposed for is adjusted for the type of material, size and condition of the item.

Examples of photographic film showing lighter areas where the object has a higher density, and darker areas where the x-rays have penetrated material which is less dense.

The photographic films then require a wet, chemical process similar to that used for black and white photographic film with a developer solution to reveal the image, followed by a fixer to secure the image and a wash to remove all chemical residues. This process takes around an hour and half and must be carried out in the dark room, with only red light, which can be a little disorientating at first!

Digital or computed x-radiography is well established and allows greater speed in reviewing and manipulating images. CMAS are actively working to move to digital, so watch this space!

How X-radiographs are used in conservation

X-radiography produces images on a 1:1 scale which allow the conservators to investigate the structure, manufacture or identity of an object. Small dark bubbles can indicate casting processes, the distinctive herringbone structure of pattern welding or wave formations of damascening are often clearly visible in x-rays, even when the surface of a blade is severely deformed.

Moreover, x-rays pass more easily through deteriorated materials and voids, these areas will appear darker grey or black compared to the brighter white of more stable areas. This can show up pitting, cracks and breaks assisting in the accurate assessment of the condition of items and their longer-term conservation requirements.

X-radiography is a non-destructive way of retrieving and revealing information and so it is commonly used in the primary stages of investigation.

Elephants and the Moon: Unexpected Wiltshire

on Tuesday, 30 July 2019. Posted in Archives, History Centre

One of the many joys of our archive is how it encompasses not only the county’s history – its people and places – but also world events as witnessed and experienced by Wiltshire folk through the centuries.

Each year I am in the privileged position of being able to take young historians on an archival journey round the world thanks to the extensive collections held by Wiltshire and Swindon Archive. These youngsters come to the Wiltshire and Swindon History Centre for work experience and for a week they get to explore the archive and local studies collections, as well as learn about the work of the conservators, archaeologists, civil registration certificates team and business support staff.

During five weeks of work placements – this year we took 14 students from six schools –the archives have transported us through time and space. We have crossed continents and centuries, catching a glimpse of the ordinary and extraordinary lives of people from another time.

As Education Officer at the History Centre there are types of documents that I frequently use because they make great classroom resources – maps, photographs, diaries, personal letters, school log books. And then there are the topics for which we have excellent collections – Tudors, Victorians, canals and railways, the First and Second World Wars and the Cold War.

But with the arrival of work experience students I have the opportunity to explore the archives at a more leisurely pace and in broader terms – and I am always finding new things to look at or seeing familiar documents in a different way. A good example is Siegfried Sassoon’s February 1933 letter predicting war. This year was the third time I produced the document for students and it was as they were practicing their transcribing skills I finally made out a word that had been eluding me all this time – ‘entente’. It was so obvious that I’m slightly embarrassed to admit that I had not worked it out sooner.

Although we often begin by digging out documents related to topics being studied at GCSE and A-Level, the challenge is to find the more unusual and quirky among them that don’t always see the light of day but which take us on wonderfully unexpected journeys.

One of the quirkiest set we produced this year concerned the gift of an elephant to Queen Charlotte (wife of George III) in 1794. Three letters (WSA 9/34/42) contain hints and allegations of an East India Company man, who acted as an intermediary in delivering the elephant, claiming back the cost of the animal despite it being a gift.

The East India Company is well documented across a number of significant collections within the Wiltshire and Swindon Archive, including archives from Wilton House, the Earls of Radnor (Longford Castle), the Seymour family (Dukes of Somerset), politician Walter Hume Long and the Money-Kyrle family.

But I was not expecting to find any further reference to elephants… Yet in the Lacock archive, among documents belonging to the Davenport family, is a cache of letters, invoices, receipts and company accounts detailing goods being shipped – including elephants’ teeth! (WSA 2664/3/2B/125 & 139 and WSA 2664/3/2D/79 et al.)

Behind the scenes at Chippenham Museum: Reconstructing Roman Ceramics

on Wednesday, 06 March 2019. Posted in Archaeology, Conservation

A number of Roman finds were recently uncovered in the back garden of Marc Allum, a specialist on the Antiques Roadshow, during excavations organised by Chippenham Museum volunteers Clive Green and Mike Stone.

Mr Allum kindly donated the finds to Chippenham Museum. The Friends of Chippenham Museum worked hard to raise funds for the conservation of one of the finds - a fine Samian ware bowl - and conservators at CMAS were privileged to undertake the reconstruction of this beautiful piece.

The Samian ware is an example of a Dragendorff type 37 bowl, suggesting it is Gaulish dating from c. AD 70-130. The bowl has intricate decorative panels with repeating motifs of Gladiators battling wild cats and a more risqué scene thought to depict the deity Bacchus.

The Samian ware was found in 51 fragments forming almost half the bowl. Due to the fine nature of the form and decoration it was decided to fully reconstruct the piece, replacing lost areas to give more complete impression of its original form.

The conservator worked hard to piece together all the fragments. Interestingly the way the ceramic had broken into layers reveals its method of construction. Samian ware with such detailed patterns was formed by pressing clay into preformed moulds. The ceramic has split along the lines of the layers that were built up.

Graham Taylor of Potted History (@Pottedhistory) has created replica moulds for the vessel and its decorative features in order to produce a facsimile using the same techniques.

Once the form of the original ceramic was determined it was possible to create an accurate profile from base to rim using measurements of the thickness of the ceramic fragments and the diameter of the base and rim, comparing these with known examples.

The profile was used to form an accurate core in clay to which the original ceramic could be secured. Plaster replacement fills were then ‘spun’ using the profile as a guide. It was decided to only replace larger areas and those smaller areas required for strength.

As Good as New... Conserved Fire Engine on Display

on Tuesday, 14 October 2014. Posted in Conservation

In late August this year CMAS conservators were privileged to work on an exciting project to conserve a 19th century fire engine prior to display at Athelstan Museum, Malmesbury. The fire engine is constructed mainly from wood, which has been brightly painted in blue and red. A large trough houses a central pump in a wooden box the whole engine sits on four chunky wooden wheels reinforced with iron tyres. Folding handles extend from the body of the engine which would be used to pump the water from its source through the machine and onto the fire. Measuring 2 metres long x 1.4 metres high the fire engine is of an imposing size. Although it is still relatively easy to manoeuvre the engine with a small team of people the response times would still have been much longer than we are now used to!

Accreditation and the Conservator

on Friday, 24 May 2013. Posted in Conservation

My name is Beth Werrett and I am a Contract Conservator for Wiltshire Council Conservation and Museums Advisory Service (CMAS). I conserve objects for and provide advice to archaeological units, museums and other heritage organisations as part of the commercial branch of the service.
A year ago I decided that, having worked for nearly five years at a variety of heritage organisations since first studying for the profession, I felt that I had developed sufficient skills, knowledge and experience to apply for professional accreditation.

What is Accreditation?

Professional Accreditation of Conservator-Restorers or PACR assesses  a conservator's professional practice within the work place. It allows a common standard to be applied across the profession, regardless of the training route taken, the conservation specialism, or the context in which a conservator may practice. An accredited conservator demonstrates a high level of competence, sound judgement and an in-depth knowledge of the principles and ethics which are key to conservation practice.

Why did I decide to apply?

The benefits of achieving accreditation were both professional and personal. For the Wiltshire Conservation Service it is beneficial to have accredited members of staff; their clients can be assured that they are working to consistently high standards.Achieving accreditation would be a significant personal achievement, providing recognition of the breadth of skills and expertise that I had developed since qualifying as a conservator. Also, I felt that the structure of continual review in place within the PACR system would help me to maintain my high standard of work and prevent me falling into bad habits!

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