MAST archaeological conservation
MAST’s unit in Poole, Dorset, is the only cradle-to-grave maritime archaeological facility in the UK capable of handling artefacts excavated directly from the seabed through the recording and conservation process to be passed on to the receiving museum. It is currently conserving all the artefacts being excavated from the HMS Invincible project and a small number from other sites such as the London in the Thames Estuary. Once conserved, the Invincible artefacts will be acquired by the National Museum of the Royal Navy (NMRN).
The Archaeological Facility, which it shares with Bournemouth University’s maritime team, is a robust industrial unit of 330 square metres converted after purchase in 2016. Vehicle access is via a 5 metre high and 4.5 metre wide roller doors. The site has full disabled access to the ground floor.
- 366m² overall area
- max 7.9m and min 6.0m eave height
- 276m² available for finds processing & passive storage
- 15m² first floor office with kitchen & teleconferencing facilities
- 30m² dive store
- 36m² general storage
- Goods access via a 5m high x 4.5m wide roller doors
- 7.2m² dive support container c/w a 195 litres/min air compressor and 135m³ air bank.
Storage volumes, the unit is capable of storing and processing
- Up to 150m² of wet finds storage
- Up to 17.5m³ of environmentally controlled storage
- 0.326m³ of cold storage
- 0.1 m³ Eurograde 2 security (max total value £175k)
Material handling. The unit is capable of handling loads / material of the following sizes
- 3,000kg @ 5.5m length
- 5,000kg @ 4.0m length
- 1,500kg palletised loads
MAST and Bournemouth University are consulting York Archaeological Trust on the conservation of the Invincible artefacts. Some of the most delicate finds were taken to YAT’s laboratory in York.
A quoin used for angling a cannon, being photogrammetised
Artefacts that we are conserving in Poole include a large number of ship timbers and wooden artefacts that made up the Georgian Navy’s “Wooden World”. These also include pulley blocks and dead-eyes of all sizes, barrels, limber boards and gun axles.
The team has also raised c.3 tonnes of rope (157 metres from the orlop deck) and c. 2,000 pieces of wadding from different bored guns (the largest collection of wadding found on any shipwreck site). These have been desalinated and washed, some then air-dried whilst brushing off excess sand. The rope will then be conserved by consolidation in diluted PEG wax solutions* and freeze-dried**. Other delicate finds include a glass bottle (intact with cork), several leather shoes.
Swivel gun conservation
Active conservation work has now begun on the five swivel guns raised in 2018. They are all currently soaking in a 2% sodium hydroxide, a solution which prevents corrosion. Meantime work has begun to deconcrete them - including the bore. Whilst cleaning one of the guns a Broad Arrow was found indicating it was indeed British government property.
Once complete, the intention is to use electrolysis to assist with the removal of the harmful salts from the iron. Electrolysis will take approximately 3-6 months, which will then be followed by a period of soaking in sodium hydroxide solutions to reduce the chloride levels to an acceptable level of less than 50ppm. Once desalinated the guns will be air dried and cleaned and will then require storage or display in a very dry environment, of less than 15% relative humidity. Treatment is estimated to last roughly two years, but this will depend upon the condition of the guns and the amount of chlorides each has absorbed. The one in the photo has a very soft outer surface which indicates a substantial loss of iron from the surface zone which often equates to a high salt content.
Ian Panter, Head of Conservation for YAT, said: “The fascinating aspect of maritime archaeology is that you are always coming across artefacts that you’ve never handled before, unlike in terrestrial archaeology where you are mostly dealing with “rubbish” discarded by its owners which is rarely in one piece. With maritime archaeology you are dealing with everyday items in their natural environment, almost a time capsule, often finding objects completely preserved as they were when the ship went down.”
One of our most prized and delicate objects is a sandglass, that counted 28 seconds, would have been used for estimating speed. This is currently being looked after at YAT.
A nautical mile was set at 6,080 ft. Knots were set 48 ft apart on the line. One knot, in speed, equates to just over 28 seconds in time. It measured an exact period when a marked log line was run over the stern, the number of knotted marks passing overboard providing a measure of the ship’s speed in ‘knots’. The circular ends are made of turned oak and the vertical posts are of pine. The artefact was perfectly intact, found on a shelf.
The sandglass is a fantastic composite object. It is very fragile and, of course, made up of multiple materials – sand glass, copper alloy, iron, twine and timber. YAT has now removed the small amount of concretion but it’s still very fragile. It presents a challenge to successfully preserve it as each component has different requirements for conservation. And their standard wood process, PEG wax impregnation and freeze-drying, may be detrimental to the glass and metal.
Ian Panter said: “We are mulling over the best way to conserve it and are talking to numerous institutions such as Texas A&M University and we also have a student actively researching the best technique to adopt.”
“The other wooden items will be straightforward. However we’ll need to X-ray the bowl and the plane to see whether any metal survives within the concretions – it’s always best practice to X-ray concretions before breaking them apart or removing them from objects. Also, the wooden bucket retains its fill and an X-ray of it will reveal whether there’s anything exciting in the contents, or it’s just sand and sediment.”
One potential problem YAT scientists are researching is the best method for conserving the Gunter scale and the folding ruler. They both have ink markings so we must ensure that the PEG wax solution won’t dissolve the numbers during the process.
*PEG, Polyethylene Glycol is a water-soluble wax, a by-product of the petroleum industry, that is used in the conservation treatment of waterlogged timbers. Once the timber is desalinated, cleaned and recorded, the object is placed in an aqueous PEG solution whose strength is increased over time until sufficient wax has penetrated into the wood cell structure to act as a scaffold, and prevent deformation of the wood during drying.
**PEG impregnated objects are dried in a freeze-dryer. Here the items are frozen to around -30 °C and a vacuum applied to the drying chamber. Under these conditions of reduced temperature and pressure the solid water – ice – is converted directly to a vapour which is then removed from the wood. This technique is a very gentle procedure as removing the water as a vapour reduces the forces applied when water is in its liquid form.
For further information on the work of the conservation team at the York Archaeological Trust, please visit the YAT conservation website or call 01904 663000 and ask to speak to either Ian Panter or Mags Felter.