Conference considers plans
for the Newport Ship
The Newport Ship in its Context
- Research, Conservation and Display
UWCN - 10th May 2003
4. Waterlogged Wood Conservation
- an Overviewby Kate Hunter
Kate Hunter in conversation with Professor Sean McGrail
at the UWCN conference.
Kate Hunter's talk dealt with the history and practicalities involved in the conservation of waterlogged wood, presenting a graphic illustration of her role as Keeper of Conservation at Newport Museum and Art Gallery, with responsibility for the care of the mediaeval ship and the other recovered artefacts.
New artefact identifications
First of all and with thanks to Dr Mark Redknapp, of the NMAGW, she announced new identifications for three important artefacts. The previously reported pieces of engraved brass strapping are decorative pieces from a military helmet, including a right cheek guard. Two other finds were, firstly a lined leather archer's wristguard with an embossed decoration of hearts, flowers and a Latin inscription, and secondly, a fragment of an hourglass which would have been used for navigation.
Conservation - Why is it necessary?
Moving onto the main subject of her talk she outlined the history of waterlogged wood conservation, describing what happens to archaeological wood as it decays. Although waterlogged wood appears to be sound, if allowed to dry out it shrinks differentially, leading to cracking with a loss of surface detail, ,warping and in the case of very degraded timbers total loss. Retention of surface detail is vital for the preservation of tool signatures etc. Prevention of warpage is important if reconstruction of any large object is intended.
Until the mid C20th treatment of large waterlogged objects presented serious problems and many have not survived. Other artefacts which had been treated with materials like alum, which decays with age, have since been retreated with PEG. Controlled air drying has also been tried, successfully with some objects, but not always. Preliminary tests on a small sample of timber from the Newport Ship, carried out by Dr Mark Jones, of the Mary Rose Trust, indicated that controlled air drying could lead to substantial levels of differential shrinkage.
The introduction of PEG (polyethylene glycol) in the late 1950's was the beginning of the development of reliable and successful treatments for waterlogged wood. The first large scale project was the spraying of the Swedish warship Vasa which began in 1962 and lasted 17 years. PEG is produced in a wide range of molecular weights which can be chosen for use according to how degraded, or not, the wood is. PEG has been used as a spray, as at the Vasa and the Mary Rose, but this method is very time consuming. The more commonly used methods are via a tanking system when the wood is immersed in heated tanks of PEG over a period of time. Or in a process known as freeze-drying, which involves some tanking but has the advantage of using smaller concentrations of PEG (a relatively expensive material) and being a shorter procedure. However, the number of suitable freeze driers both in the UK and elsewhere is limited and that presents a time constraint in itself. Both tanking and freeze-drying produce good results, although freeze drying produces a wood which is lighter in weight, and usually colour, after treatment.
Before any treatment is decided it is necessary to carry out a condition assessment. Quoting Jim Spriggs of the York Archaeological Trust "Before any suitable conservation regime is applied to wood it is necessary to quantify where possible, the level of decay suffered. Only then can the correct treatment regime be constructed to take into account the loss of material from the cell structure or 'wood substance' as it can be described."
The Newport Ship
At this stage nobody knows how the ship will be conserved. A detailed condition assessment has yet to be undertaken which would normally require a large number of samples to be taken at different levels over the whole length of the ship. Sampling could be integrated with an archaeological research programme, for instance dendrochronology, as was done with the Barland's Farm boat. In the choice of treatments for the Newport Ship there was a real advantage because the ship had been taken apart piece by piece, so that timbers could be individually treated and a full range of conservation processes was available. Miss Hunter stressed, however, that no treatment could be guaranteed 100% effective, and that in similar projects detailed recording had taken place in advance of treatment. Additionally once conservation treatment commenced timbers were less easy, if not impossible, to access.
In brief for a project of this scale:
- A condition assessment will be needed before a choice of conservation treatments is made. This could be coordinated with other archaeological research.
- Before treatment begins some level of recording must be completed. Close liaison with the archaeologists is necessary throughout.
- The facilities offered by Corus were excellent for recording but not at present for the treatment process.
- Whatever the final preferred conservation option, there remains the question of where it will be done.
Kate Hunter, is Keeper of Conservationat Newport Museum
& Art Gallery and has responsibility for the care of the
timbers and other artefacts recovered with the ship.
Summary of the presentation prepared by Ron McCormick
10th June 2003
Individual papers
1. "Need the excitement be a nightmare?" by George Lambrick
2. Excavating the Ship by Kate Howell
3. The Wood Record by Nigel Nayling
4. Waterlogged Wood Conservation - an Overview by Kate Hunter
5. The Post Excavation Process by Sean McGrail
6. Future Planning Considerations for the Newport Ship by Gustav Milne
The Newport Medieval Ship in its Context
- Research, Conservation and Display
Saturday 10th May 2003
University of Wales College Newport
Caerleon,
Newport,
South Wales, UK
Organised by UWCN in association with
the Friends of the Newport Ship
and Chepstow Archaeological Society