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.
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.
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.
Quite often I come across interesting things as I go about my business in the strong rooms at the WSHC. Today was no exception when I discovered this rather odd-looking book. On first glance it appears that someone has rather hurriedly wedged a large book into a small bag but on closer inspection I discovered I was looking at a medieval chemise binding.
The binding contains an Act and Memoranda Book for the Tailors’ Guild of Salisbury including byelaws, admissions of freemen and apprenticeship indentures, dating from 1444-1838 and gives us a wealth of information regarding their organisation and activities.
It is big and extremely heavy and has a particularly large piece of leather skirting along the tail edge (lower edge). It has visible sewing stitches along the edges and two metal clasps on the foredge (front edge) that attach to corresponding slits in the cover. The book dates from 1444 so is most likely an original medieval binding, although more recent sewing repairs are visible around the edges. The text block pages are made from parchment and contain varying manuscripts, some with illuminations.
A new project recently appeared in the archive conservation lab: a brittle and damaged looking document that turned out to be an interesting new accession.
Letter Sent to Francis Yerbury, 14th May 1747 (1387/1697)
The document is a letter sent to local Clothier Francis Yerbury in 1747. It is thought that he may have run a cloth mill in Trowbridge although the letter is about a mill in Bradford-On-Avon. Hanne Dahl, Exhibitions and Collections Officer at Trowbridge Museum has transcribed the letter and below gives an overview of the its content:
The letter seems to consist of two messages. One is regarding a cloth order which John Howell has received and is ensuring Francis Yerbury he will pay for. The other is a new cloth order for the Empress of Russia of Clergy cloth in scarlets and greens. 5 cloth samples of Yerbury’s are attached to the letter as a colour reference. The Empress mentioned was probably Elizabeth of Russia who lived 1741-1762. According to popular history clothing was the chosen means in Elizabeth’s Court by which to display wealth and social standing and according to historian Mikhail Shcherbatov (1733-1790) her court was “arrayed in cloth of gold, her nobles satisfied with only the most luxurious garments, the most expensive foods, the rarest drinks, that largest number of servants and they applied this standard of lavishness to their dress as well.’ Hanne Dahl, Exhibitions and Collection Officer, Trowbridge Museum April 2019
The new accession was passed on to the archives here at WSHC by Hanne after being in the care of the Ponting family; the late Ken Ponting being former Managing Director of Samuel Salter Ltd. weaving mill in Trowbridge.
As is often the case with the documents I work on, there is much of historical interest and I could spend many hours researching them. However, as a conservator, once I have enough detail to inform my conservation decisions, I must tear myself away from the fascinating historical insight and prioritise stabilising and preserving the letter so that future researchers can access it safely.
It was originally folded to be posted and has the postal address visible on one of the folded sections. The letter is written in brown ink and has textile samples and a small part of a wax seal attached.
Several factors made this a conservation challenge; not only was the paper extremely thin and fragile but the additional attached textiles samples and seal remains also had to be considered at all times as they could easily become detached and lost.
The document needed to be packaged so that it could be safely stored in the archive but also handled without the risk of further damage. As the paper was so thin, it could easily tear again with further handling, even after conservation.
I decided that once repaired, the document would be safest inside a mount- this would allow for compensation of the thickness of the attached textile samples and seal remnants as the depth of the window mount would prevent them getting squashed or dislodged in storage. It would also enable easy viewing as and when required without direct handling of the letter. Text found on the back of the letter was all in one area so the mount could be adapted to have a viewing window on the reverse. This would also mean the document didn’t need to be taken out of the mount or handled to see this.
Areas of damage on the letter
The letter arrived with us inside a frame, attached to a backing board with tape partially holding it around some edges. The paper was so thin and weak that tears had started to appear along many of the original fold lines whilst large areas were breaking around the edges. It was important to remove the letter from the backing for several reasons; the backing board itself, made from poor quality board was likely to be causing damage to the paper. Unless they are archival quality, backing boards and framing materials are often made of very poor quality materials with high levels of acidity. As these materials break down they can transfer acidity to materials they are attached to, increasing their deterioration. I also needed to access the document to effectively repair the tears and remove the adhesive tape.
I was able to successfully remove the letter from the mount using a spatula to ease the tape away from the board surface.
When the board was removed it was possible to clearly see acid transfer which appeared to be coming from the document and transferring onto the backing board, suggesting the paper itself is acidic. This is likely to be due to the ingredients used when the paper was originally made, for example additives such as sizing and fillers or the materials the paper is made from such as wood pulp. The ingredients vary between paper mills and throughout the history of papermaking, for example Lignin from wood pulp is extremely acidic and is generally found in modern papers such as newsprint. This is what makes newsprint go yellow and brittle so quickly.
After removing the document from the backing a new area of writing was discovered where the letter had in fact continued overleaf. The archivist was then able to add this to the existing transcription.
Once the letter was separated from the backing board I could then remove the adhesive tape. This task of removing tape is always daunting for a conservator as different adhesives react completely differently to different types of removal. Sometimes it can take a long time to find a method that softens or releases the adhesive so that the tape can be removed.
On this occasion I found that applying moisture directly onto the tape was enough to release the adhesive. However, a thick piece of brown adhesive tape down the left side of the letter was so stubborn that after removing a small amount I decided it would be better to leave that particular piece of tape on rather than risking damage to the already fragile paper surface.
Once the tape had been removed I surface cleaned the document being careful to avoid any weak areas. I was then able to move on to repairing and stabilising.
Tears on paper documents are generally repaired by adhering small pieces of Japanese tissue to the reverse.
The tissue I used for the letter is only 5 gsm, so it is extremely thin and light- but strong enough to stabilise the tears and weak areas without distracting from the letter itself.
Two areas of the document had large gaps that although supported on the back with the Japanese tissue repairs, needed to be infilled with a paper of a similar thickness to the letter itself, to prepare the document for mounting. In the conservation of archival documents (as opposed to artworks) it is particularly important that repairs such as this are visible additions, clearly seen as modern repairs and not blended to make them invisible. This ensures that future historians and researchers are aware of the difference between the original document and any conservation work that has been done.
Creating an Inlay
In paper conservation an inlay is a piece of paper that is attached around the outside of the document to protect it and prevent further damage to fragile edges. This is achieved by tracing around the edge of the document using a needle and then removing the inner piece of inlay paper to create a paper frame. The inlay paper is attached to the document by thin strips of Japanese tissue adhered along the gap between the two. The inlay protects the original document whilst still retaining full visual access to it. It also means that the document can be attached inside the mount by putting hinges on the inlay paper rather than directly on the document itself and that the letter can be fully displayed in the aperture of the window mount without falling out through the middle.
Having reached the milestone of 10 years in my current place of work, I have been reflecting on the development of my career. I think my greatest fear as a conservator is stagnation: for my work to have lost its vibrancy and draw, for my relationship with my career to have become stale.
Thankfully, even after a decade I still find daily challenges and opportunities to develop and thrive within the sector. The importance of Continuing Professional Development (CPD) is emphasised within the conservation arena; viewed as integral to the maintenance of professional standards by organisations such as ICON, the Institute of Conservation.
Being an accredited conservator (ACR), maintaining CPD is essential to retaining my accredited status.
The CPD format encouraged by ICON allows conservators to reflect on where they have come from, focusing their aims for the future. Through a candid analysis of the strengths and weaknesses within both my team and my own armoury I was able to identify a need to improve specialist knowledge of the care of natural history specimens.
The generous award of a True Vue professional development grant allowed me to secure a place on an intensive 3 day course focusing on the care and conservation of vertebrate taxidermy specimens with Simon Moore, a subject specialist with 50 years experience.
The 3 day course kindly hosted by Reading Museum allowed experience of a broad range of materials and techniques. From the art of opening historic glazed cases, without which you’d never access the specimens; to the cleaning of feathers, repair and replication of birds toes and the creation of hair plugs for a balding otter!
The course created a relaxed welcoming environment in which I felt able to voice my previous anxieties about tackling such materials from the risk of shattering historic glass to fears of using the wrong materials and my work ending in a terrible taxidermy publication!
The natural history collection at Reading Museum is extensive and allowed course attendees the irreplaceable opportunity to put theory into practice.
Corrosion that appears on metal objects is a chemical reaction where the metal is trying to return to its natural mineral state. This often appears as green deposits on copper and red/brown deposits on iron. The main cause of corrosion on metals is a humid environment.
How do you remove corrosion?
Some corrosion is good! If your metal object has a thin dark layer on the surface this may be acting as a protective barrier from further break down of the surface. This is called patination or tarnish.
We would recommend you avoid trying to remove heavy build-up of corrosion yourself. This often needs to be done under a microscope in controlled conditions. Excessive use of polishes and chemicals (I’m including Cola and Ketchup in this!) could remove original surface so that details and decoration are lost. For example, you would no longer be able to identify the date of a coin if the surface was abraded and removed. It can also cause the metal to thin and wear down silver plating. Chat to a conservator if you are concerned about the corrosion build up on your object or want to find the most suitable cleaning regime.
How do I care for the object in the future?
One of the most damaging things to metals is the oils and acids from our fingers, which can etch in to the surface of the metal. We would recommend always wearing cotton, nitrile or latex clothes when handling metal objects. This will also reduce marks and therefore the need for cleaning.
Giving the metal object a dust with a soft micro-fibre cloth or soft hog or pony hair brush will help prevent build-up of dust and dirt. Buffing or coating the surface with wax should rarely be necessary and should only ever be attempted after removing dust and dirt. Depending on the object and environmental conditions a wax or lacquer may be applied to protect the surface from humidity and prevent future corrosion development.
Store in an environment with a low humidity and pack using inert materials such as foam or acid free envelopes. A hoard of coins recently in conservation was packaged in individual acid free paper envelopes, sealed in a Polypropylene plastic box (recycling number ‘5 PP’) to provide a controlled environment and a sachet of silica gel to reduce humidity.
So, remember, avoid the cola and gently brush your objects to maintain a healthy patination!
Kayleigh Spring, Conservator, Conservation and Museums Advisory Service
Wiltshire Conservation and Museums Advisory Service is based at Wiltshire and Swindon History Centre. We preservice the Wiltshire and Swindon Archives and provide support to museums, heritage organisations and individuals to care for and conserve historic collections and meet professional standards.
If you have items in need of a little TLC see if our conservator can give you hints and tips for cleaning without damage, advice on storage or a to get a quote to have them repaired.
We hold regular conservation surgeries at WSHC from 2 – 4pm on the second Thursday of every month. The next one will be on May 9th. Book you appointment by calling 01249 705500.
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.