Page 52 - TVH 2000 Anniversary Shipwreck Project

Conservation Ton Van der Horst Procedure As soon as the vessel docked all finds were transported to the conservation facility at the Stedelijk Museum in Vlissingen. They are cleaned and separated into material types before conservation. Any unphotographed artefacts are photographed. Anything missing from the artefact registration form is added at this stage. Wood and leather are placed immediately into a large freezer, or tank containing fresh water if they are too large for the freezers. Once the organics have been frozen, water is removed by placing them in a vacuum freeze-drying chamber (Edwards BF 4) which can extract 1.2 kg of ice in 12 hours. After freeze-drying, wooden artefacts are treated with linseed oil to prevent any further drying or collapse. Leather is freeze-dried, but a specific leather dressing is applied once they are dry. If possible, reconstruction is undertaken at this stage. Both complete and incomplete wine bottles are washed in tap water, as are all glass artefacts. This is undertaken within a circulation tank where the water is filtered. Routine readings for chlorides are taken. When the reading is stable, suggesting that there are no more chlorides within the glass, the artefacts are washed in distilled water until the chloride reading is less than 20 parts per million. The glass is then dried and immersed into a 1/10 solution of Dormoplast SG Normal that provides a coating. Any corks are treated with a two-part glue to prevent shrinkage. Earthenware, stoneware and porcelain are washed in distilled water and dried. After each excavation season all the fragments from each trench are gathered together to try and piece together any vessels. Bronze, silver, copper, brass and pewter are cleaned in an electrolytic tank using a 5% sodium hydroxide solution with the object forming the anode attached to a stainless-steel cathode. A 5 volt electrical supply is used. Following electrolytic reduction, the objects are neutralised and cleaned ultrasonically at between 40 - 70 degrees centigrade by turning a power supply on an off in intervals of not longer than five minutes. This short interval is necessary to prevent cavitation occurring which could damage the object. After the object is dry it is lacquered with Pantarol. Gold is cleaned in an 85% solution of nitric acid, neutralised, ultrasonically cleaned and dried. Steel and cast iron are treated by immersion in a 63 gram per litre solution of sodium sulphite which is covered and heated to 70 degrees celcius and constantly mixed. The solution is changed weekly following routine chloride readings. Once the readings remain below 100 parts per million, the objects are considered stable. The remaining chlorides have changed into barium sulphate. The object is then dried and placed in melted microcrystalline wax. Reconstruction All incomplete objects are studied with their associated objects. Any broken objects which can be reconstructed are put together. Objects which have been damaged or bent such as pewter plates are carefully reconstructed to show their original form and placed on display to tell their own story. Photo 37 shows reconstructed lanterns from previous excavations and a conserved oil lamp from the 2000 season. - 46 -