CONSERVATION

The conservation department is responsible for the care and protection of Ashmolean objects. We have dedicated teams and techniques for the conservation of paper, textiles, objects and paintings. Each conservation project reveals a new side to an object. By using methods such as x-ray, radiography and RTI technology we get a 360-degree view of what lies beneath the surface of some of the most prized objects in our collections.

INVESTIGATIVE TECHNIQUES

Modern technology continues to provide a range of sophisticated tools for the understanding and preservation of our cultural heritage. Conservators are often in the privileged position of being able to examine an object in close detail, using many different tools to examine and investigate their condition, composition and history. Beginning with simple examination under magnification, this can lead to further investigation using a range of techniques. This helps to understand how an object was made and used and also helps the conservator design a treatment or preservation plan.

The following techniques and equipment have been used to examine and investigate objects in the museum. Some of the equipment mentioned in this section belongs to the museum and some has been used with the generous assistance and collaboration with scientific departments in Oxford University and beyond. 

Using an endoscope to look inside a sculpture
Using an endoscope to look inside a sculpture
ashmolean conservation
Using a microscope to examine fine detail

The microscope is the primary investigative tool of conservators, enabling them to observe details of an artefact. It reveals dirt, damage (whether recent or ancient), cracks and evidence of use and of original technology, such as incised decoration and gilding. Also revealed on metal artefacts is the presence of mineralised organic remains of flesh, textile or hair. Higher magnifications are used to reveal more information, such as the identification of the weave of a textile and the differences between types of pigments and media, fibres, wood and other materials.

Detail x18 magnification (microscopy)
Detail x18 magnification
Pen and ink drawing by Samuel Palmer at the ashmolean museum
Pen and ink drawing by Samuel Palmer

Cross-sectional analysis (or stratigraphic examination) is a standard technique for looking at the layers in a micro sample. In particular it is used in the examination of paintings where it can allow us to look at the layers of priming, paint, varnish, dirt and restoration in the order they were applied. It is also possible to begin visually identifying the contents of each layer before passing the sample on to other specialists for further analysis if necessary.

By dispersing the contents of a micro sample of paint, it is possible to look at the pigment particles under a polarised microscope. Individual features of the pigments enable us to identify a number of the most commonly used paints.

A cross-section (x 500 magnification) of a micro sample
A cross-section (x 500 magnification) of a micro sample
Landscape with the Repose of the Holy Family by Samuel Palmer at the ashmolean
Landscape with the Repose of the Holy Family by Samuel Palmer

Light shone at an angle across the surface of an object is called raking light, and the shadows that are cast show up any surface irregularities. When light is shone through an object from the back, it is called transmitted light. This is used to reveal flaws in gems and watermarks in paper.

In transmitted light showing chain and laid lines of the sheet, and old repair (showing black).
In transmitted light showing chain and laid lines of the sheet, and old repair (showing black).
Agostino Ciampelli (1565 -1630) Studies of Three figures, in direct light at the ashmolean museum
Agostino Ciampelli (1565 -1630) Studies of Three figures, in direct light

Infrared (IR) light is not visible to the naked eye but if a painted object is illuminated with IR, the paint layers appear more transparent than with normal (incandescent) light. This enables underdrawings, signatures or inscriptions to be revealed. This new information can be recorded by photographing it with IR-sensitive film.

Lorenzo di Credi (1457 - 1536), Virgin and Child. Infra red light image shows under drawing.
Lorenzo di Credi (1457 - 1536), Virgin and Child. Infra red light image shows under drawing.

Ultraviolet (UV) light is invisible to the naked eye, but it can be useful since UV directed at certain substances, such as resins, will cause them to glow (fluoresce). This can reveal repairs, tears in canvasses under darkened varnishes, and overpainting (as old and new areas fluoresce differently). Even areas of paintings or manuscripts where pigments have faded or been lost can be enhanced. UV also has uses in the examination of wood, ceramics and other materials, but as it is damaging, it is only used for very short periods of time for investigative purposes.

Under ultraviolet light showing previous joins and restorations.
Under ultraviolet light showing previous joins and restorations.
ceramic bowl from Iraq (AD 900 - 1000) at the ashmolean museum
Ceramic bowl from Iraq (AD 900 - 1000)

Analytical investigation allows us to answer further questions about an object using a range of more sophisticated equipment. The types of analytical techniques can be divided into two main categories:

  • non-destructive techniques where a sample does not need to be removed from the artefact for analysis
  • destructive techniques where a small sample is removed from the artefact for analysis.

We increasingly use non-destructive techniques or techniques that use smaller and smaller samples, taken from a discrete area. A judgement has to be made whether the information that can be gained is worth removing a small sample from the object. 

Analysing a bronze painted plaster cast using X Ray Fluorescence equipment (Cranfield University)
Analysing a bronze painted plaster cast using X Ray Fluorescence equipment (Cranfield University)

 

Conservators use X-radiography (X-rays) on artefacts ranging from coins to mummies and paintings. The X-rays penetrate materials at different rates. It is the density, rather than the thickness, of the object that determines the strength of the X-ray used and the quality of the image produced. Just as in medical use, X-rays reveal the structure beneath the surface of an object and this can provide the conservator with useful information, such as:

  • metal structure: indicating the technology used in manufacture; different metals used in construction; details of decoration hidden by corrosion
  • mummies: revealing breaks and cracks which indicate fragile areas; the presence of amulets; different burial practices; bone structure indicating gender, age or illnesses
  • ceramics: structure and technology used in manufacture; contents, such as cremation remains in funerary urns
  • paintings: structure; preparatory drawing; underpainting; presence of lead pigments; previous repairs
X – radiograph ashmolean
X – radiograph
mummified ibis at the ashmolean museum
Mummified ibis

 

Computed tomography (CT) scanning uses X-rays to build up a picture of the inside of an object in "slices" which can be manipulated to give a 3-dimensional view. The technique was developed for medical diagnostics but has also been applied for use on  museum collections. It allows mummies to be investigated without unwrapping them, as well as fragile metals and other materials.

One of the scans showing the child probably died of pneumonia.
One of the scans showing the child probably died of pneumonia.
Egyptian child mummy (died between AD 80 - 120) entering CT scanner
Egyptian child mummy (died between AD 80 - 120) entering CT scanner

 

This is mostly used for recording the watermarks in paper, especially where the mark is obscured by printing or drawings. The paper is "sandwiched" between a sheet of plastic that has been impregnated with a radioactive form of carbon and a sheet of film that is sensitive to the radiation given off. It is left in darkness for several hours. Radiation passes from the carbon impregnated plastic through the paper to the sensitive film. More radiation can pass through the area of the watermark because the paper is thinner at that point, and so an image of the mark is made on the film.

Rembrandt van Rijn (1606 - 1669): The rat catcher at the ashmolean museum
Rembrandt van Rijn (1606 - 1669): The rat catcher
Watermark in the paper used by Rembrandt.
Watermark in the paper used by Rembrandt.

Fourier Transform Infrared Spectroscopy (FT-IR) is a method of analysing the composition of organic materials based on the fact that every chemical bond has a characteristic energy level. In FT-IR an infrared laser beam is focused on a small sample from the object, which then absorbs energy. The energy that has not been absorbed is detected and displayed on a graph (spectrum) as a series of peaks. These peaks each represent particular chemical bond energies, enabling a conservation scientist to identify the chemical structure of the sample.

FT-IR analysis of picture varnish
FT-IR analysis of picture varnish

X-Ray flourescence (XRF) is also based on characteristic energy levels. Here, it is the energy produced when an X-ray beam directed at the object causes the electrons (negatively charged particles) in an atom to jump to a higher energy level. As the electrons return to their original state they release energy characteristic to that element. This is detected and is used to determine the elements present. XRF is used mainly for the identification of metallic elements such as the quantities of silver, copper, and lead in a coin.

Objects being analysed using bench-top XRF equipment
Objects being analysed using bench-top XRF equipment
Analysing a bronze painted plaster cast using X Ray Fluorescence equipment (Cranfield University)
Analysing a bronze painted plaster cast using X Ray Fluorescence equipment (Cranfield University)

Optical microscopes use lenses to focus light to produce a clear magnified image. Similarly, SEMs use electromagnets to focus a beam of electrons that is directed at a sample. The focused electrons are detected and displayed on a screen. SEM is useful to conservation as it provides a greater depth of focus and higher magnification than the optical microscope and analytical equipment can be attached for the identification of chemical elements.

SEM image identified as algae.
SEM image identified as algae.
Figure of a standing woman, anonymous, French at the ashmolean museum
Figure of a standing woman, anonymous, French

Sometimes questions arise when examining an object that can challenge its authenticity. Using investigative techniques it is possible to uncover a full range of intentions from honest restorations that are hard to tell with the naked eye, to deliberate deceptions for the unwary buyer. 

The glass bowl (below) was bought in 1882 and given to the museum as a Roman or Hellenistic original. It soon deteriorated even under stable conditions. Investigative techniques, including XRF, showed a composition unknown in ancient glass with almost no calcium oxide stabiliser. It may have been deliberately made unstable to imitate weathering of ancient glass. 

fakes conservation ashmolean
fakes conservation ashmolean

 

CONTACT US

Tel: +44 (0)1865 278024
Email: conservation@ashmus.ox.ac.uk 

Head of Conservation: Daniel Bone
Objects Conservator: Liz Gardner
Objects Conservator: Paulina "Nicky" Lobaton
Objects Conservator: Stephanie Ward
Paintings Conservator: Jevon Thistlewood
Senior Paper Conservator: Alexandra Greathead
Paper Conservator: Lara Daniels
Paper Conservator: Beth Twinn
Preventive Conservator: Kelly Domoney
Project Conservator: Sue Barker
Textile Conservator: Sue Stanton
Administrator: Sean Weston

 

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