In 2003, preventive excavations carried out at the request of the government by a team of Inrap archaeologists in the Saint-Georges neighborhood uncovered 16 ships including a second-century barge likely used for trading along the Rhone River.
Owned by the Metropolis of Lyon, the barge will be exhibited in the Gallo-Roman Museum of Lyon-Fourvière. For this, it underwent a complete restoration under the joint supervision of an archaeologist from Inrap and a restorer from Arc-Nucléart.
Different treatments for wood and metal
As part of its conservation, the barge was first placed in a 200 square meter workshop with an atmosphere whose temperature and humidity are perfectly and continuously controlled.
The wreck included a large number of metal nails, the source of the formation of pyrite, an iron sulfide that in humid conditions produces sulfuric acid which may eat into the wood. A treatment distinguishing the wood and metal parts was thus initiated.
Dismantling a boat in 1,000 pieces
In 2003, Inrap's archaeologists found 17 meters of the barge which probably originally measured 28. The complete dismantling of the boat (nearly 1,000 individual pieces) was undertaken with precise labeling to ensure that they could be reassembled. The various components could then be examined to understand how the boat was used and maintained. Thus the archaeological dendrochronologists* were able to identify and date the types of wood composing the barge, while the traceologists* studied the traces left by tools that were used to produce them. The rigorous dismantling and study generated three times the archaeological data from a traditional restoration of similar objects, thus greatly enriching historical knowledge of the period.
The metal parts, including 2,100 nails, were removed one at a time. The nails will be studied to determine the source of the metal and how they were produced.
Soaking wood to eliminate water
To treat the wood, Arc-Nucléart applied two techniques which its teams alone are capable at this scale.
After having removed the metal compounds using a gentle cleaning, the parts made of wood were thoroughly soaked with a polyethylene glycol (PEG) resin. The treatment, which lasts a year, in part replaces the water contained in the wood fibers with PEG. Lyophilization is used to dry the pieces without losing their shape. Arc-Nucléart is one of the few laboratories in the world that can carry out such a process while continually recycling large quantities of PEG.
Ionizing radiation used to harden wood
In addition to the previous treatment, part of the ship, which is greatly damaged, was soaked with another resin (styrene polyester), and subjected to gamma radiation. The radiation caused the resin to polymerize, thus hardening the piece of wood. Once it was sufficiently solid, the piece could be reassembled with the other parts of the boat. Only Arc-Nucléart is capable of applying this Nucléart process.
On September 20, 2016, after validation of the assembly by the scientific committee assigned to the boat, the restored wreck will be once again dismantled and placed in a controlled atmosphere on a specially designed support.
The barge, since renamed Lyon Saint Georges 4, will later be transported and installed in a room with a controlled atmosphere in the Gallo-Roman Museum of Lyon-Fourvière, where it will be on exhibit for visitors and researchers.
About Arc-Nucléart
Founded forty years ago to preserve historical artifacts and conserve archaeological remains from sublacustral excavations, ARC-Nucléart in 1997 officially became a cultural public interest group under the supervision of the Ministry of Culture, CEA, Auvergne-Rhône-Alpes Regional Council, City of Grenoble, and ProNucléart. Located at the site of CEA's research center in Grenoble, its mission is:
- conservation and restoration of objects composed of organic materials (wood, leather, fibers) produced by humans in all fields of endeavor,
- research deteriorated materials and develop new treatment methods, which may also be applicable to recent wood.
Such fragile, historically significant artifacts must undergo operations to strengthen and restore them for conservation and public exhibition. In a 3,000 square meter facility of high tech equipment, a multidisciplinary team (chemists, physicists, technicians, restorers, conservators and administrative staff) works to preserve France's physical heritage in museum collections and historical monuments as well as during excavations, where they assist archaeologists.
www.arc-nucleart.fr
About Inrap, the French National Institute for Preventive Archaeological Research
With more than 2,000 employees and researchers, Inrap is France's largest archaeological research organization and one of the foremost in Europe. A national research institute, it carries out 1,500 archaeological diagnostic examinations each year and 250 excavations in partnership with private and public developers in France and its overseas departments. Its missions include the scientific use of the results and expanding the public's knowledge of archaeology.
www.inrap.fr