Preserving a Shipwreck (The Cog) by using deionized water


How does Flanders Heritage Agency go about getting it to look like it did before it spent 7 centuries underwater?

The cog discovery – a brief history.

In 2000 a shipwreck was found in the Deurganckdock in the Antwerp harbour (Belgium) - During excavation works - which was identified as a cog and dated to 1325. Every fragment of wood is tagged with a unique code and stored in containers filled with tap water.

In 2009: The Flemish Minister for Immovable Heritage, Geert Bourgeois, gives VIOE (the Flemish Institute for Immovable Heritage) the task to carry out research on the cog remains.

What is a cog? Historical significance.

The cog is a medieval European ship type which is thought to have originated in the North Frisian tidal flats. The oldest can be traced to the 11th century Denmark. The cog is a wide, flat-bottomed ship with a straight stem and stern and high sides. The cog was in use on the European seas as a merchant ship and occasionally as warship. It had a large part in the flourishing economy of the late medieval towns such as Bruges, Ghent and Antwerp in Belgium.

The cog project. Restoration, preservation and research.

In the summer of 2010 a large scale research on the archaeological remains focusses on several aspects of the ship. Every piece of timber is measured and analyzed with attention to use, fabrication, tool marks and wear. All 455 ship parts are being digitally 3D recorded with a Faro-arm. These Rhinoceros files will be used to construct a replica of the cog in sintered polyamide on scale 1:10.

Sciences such as dendrochronology, palynology, paleo- and archaeobotany and tar analysis are necessary to determine the life cycle of the ship.

In 2011 a large survey was set up to investigate the condition of the wood. Based on the results the preservation process of the ship starts in view of its reconstruction and public display.

The condition survey is carried out by the conservators of the Flanders Heritage Agency in cooperation with the conservation department of the National Museum of Denmark. First the condition of the material was assessed to determine the degradation of the wood. The second part of the survey assessed the structural condition. The mechanical damage of the fragments such as fragmentation, cracks, holes from sampling, etc. was recorded.  This information is essential for the reconstruction and the design of a support frame and the future display of the ship.

The condition assessment shows that the wood is degraded.  Drying waterlogged wood without pre-treatment in an uncontrolled way would cause irreversible damage.  Since 2012 measures were taken to start the conservation process of the ship.

Induss’s role in the conservation process.

During the first phase of the conservation process the wood
will be desalinated because of the large amount of inorganic material (iron, calcium and sulphur) detected in the wood cells.

These ions could cause complications for the stability of the wood during the exposition of the ship. 21 containers filled with demineralized water , from Induss’s bulk water load station in Antwerp, mixed with a small amount of di-ethylene penta-acetic acid (DTPA) and hydrochloric acid (HCl) will be used to diffuse ions out of the wood. 

Afterwards the archaeological wood will be impregnated with polyethylene glycol 2000 (PEG 2000). This method replaces the water in the wood cells with PEG 2000 as a consolidant or bulking agent. PEG prevents the wood from shrinking by preventing the collapse of the cell structure. When the desired concentration of 85 % of PEG is reached, the ship will be ready to be air dried in a controlled museum environment. 

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