THE MA'AGAN MIKHAEL SHIP - THE END OF THE CONSERVATION PROCESS
The conserved keel in its tank. (Photo: R. Pollak)
On June 20, 1996, the conservation process of the keel of the Ma'agan Mikhael ship reached completion. It was the last of the ship's timbers to reach this stage, with conservation taking more than four and a half years. The keel is a single piece of pine wood 8.26 m long, 16 cm molded and 10.5 cm sided. It is rockered by a few centimeters and rests on its side in a stainless steel tank that was especially built in order to retrieve the keel intact from the sea bottom and hold it during conservation. The tank is 10 m long, 45 cm wide and 25 cm deep, with three rectangular tunnels, each 7.5 cm wide and 3 cm high, installed on the inside of its base and running almost its entire length. These fixtures prevent the wood from resting directly on the bottom plate of the tank.
The keel was retrieved on December 19, 1989, the final day of the excavation. More than a year later the conservation systems were installed in the tank. These included four heating elements of one kilowatt each, air pipes for mixing the solution and control and safety sensors. The metal tank was insulated using a double layer of 5 cm thick polystyrene.
Conservation of the keel took place in two stages due to its dimensions, although the process, using 100% PEG, was essentially the same as for all the wood recovered from the Ma'agan Mikhael ship. The first stage involved the use of liquid PEG 400 to a 45% concentration and the second, PEG 4000 (E 3350) to a concentration of 100%. The average rate of introduction of the PEG was one percent per week, beginning on December 25, 1991.
On April 25, 1995, at the time of the extraction of the mast step, the conservation value of the thick wooden elements, including the keel, was measured. A reasonable PEG penetration of the keel was found, but we decided nonetheless, to prolong the conservation process. At this time, the thinner planks of the ship had already been in storage in a controlled temperature and humidity room for two and a half years, while the thicker timbers had been stored for more than a year.
The decision to continue the conservation of the keel was made taking several things into consideration. We wanted to be sure beyond any doubt that the keel was properly conserved and thought (perhaps incorrectly) that the longer the conservation process, the better the result. We had yet to design and install a controlled air system for seasoning the keel once the conservation process reached termination, and although the exhibition hall of the new museum was at a stage of advanced planning, construction had not yet begun.
A serious problem was revealed as we neared the final stage of conservation. We had been concerned for a long time regarding the formaldehyde gas extracting from the 60°C hot PEG. Tests proved that we were exposing ourselves to approximately double the permitted amount of this dangerous gas. University authorities were immediately informed and work was ceased in the laboratory until an improved air ventilation system was installed.
Towards December 1995, we tackled the problem of how to store the conserved keel for seasoning. The drying method and the design of the air conditioning system were determined by one major factor - the fragility of the wood. Although the keel could be retrieved from the tank, and at great effort and expense, stored in a specially prepared hall, we could not risk damaging the 2,400 year old, soft and fragile wood. We observed that a solid layer of PEG had been consolidated on the bottom of the tank cementing the keel to it. Rather than harm the keel, after six and a half long years of treatment, we decided to dry it in the conservation tank. The problem of its underside attachment by solid PEG to the bottom of the tank will be addressed at a later date, perhaps at the time of the ship's assembly in the museum. Therefore, instead of retrieving the keel from the tank as was done with the other pieces of wood, the PEG was rinsed out of the tank and the tank modified for storage. The existing air-conditioning systems, servicing the two storage rooms housing the conserved timbers, were extended by the use of air pumps to the point where they were capable of supplying monitored air to the keelÕs tank. The system was organized so that each air-conditioner operated independently and could compensate for the other in the event of a malfunction. This was all achieved at minimal expense.
Nearing the date set for the drying of the keel, we found that the PEG had, for some reason, changed its character. It had become a darker brown, remained sticky for a longer period and took a longer time to harden. We submitted a sample for analysis but have not yet received the laboratory report. Our assumption is that over a short period of time, the PEG degraded to a considerably lower molecular weight. We were forced to take certain measures in order to ensure the results of the conservation. We replaced all the PEG in the tank with used, but undegraded PEG and some new PEG. Deposits found on the wood and the tank bottom were cleaned, and the temperature was kept as close to 60°C as possible. We had no choice but to extend the conservation process for an additional five months to make sure that the PEG absorbed into the keel was of a consistently good quality.
Although the process of drying the keel took only one very long working day, the procedure had to be planned well in advance, and precise preparations made. The aim was to rinse off the PEG and dry the wood, causing minimum damage and trying to anticipate any problems before they arose.
Preparations for the drying process included: modifying the air-conditioning system, making a new cover for the tank, and replacing the heating elements with elements capable of heating the solution even when it reached levels as low as 10 cm from the bottom of the tank. All additional pieces of wood that had been conserved together with the keel in the tank, were retrieved and wiped of the excess PEG.
We began the actual drying process by pumping the PEG into another tank until the level in the keel tank was reduced to 2 cm below the surface of the keel. The excess PEG was carefully wiped off the exposed wood. At this point, the upper surface of the wood was allowed to cool and dry while the lower part remained submerged in hot PEG. This measure was taken in order to minimize the downward movement of the PEG and shrinkage of the upper surface of the keel. After a two hour drying period, the level of the PEG was dropped by another 2 cm. Once again the wood was wiped of the excess PEG and left to dry for an hour. During the third step we again dropped the PEG level, uncovering the heating elements which had been lowered previously. The heating system was shut down and the elements removed from the tank. Finally, the last of the PEG was pumped out and we were left with the longest and most exhausting job - wiping the excess PEG off the keel, cleaning the tank of the PEG residues and establishing the correct temperature and humidity settings in the tank.
After hours of work with this hot, sticky, substance, somewhere between a liquid and a solid, we were left with the complete conserved keel resting in its tank, clean of PEG and ready to begin its seasoning period. Shrinkage will be carefully monitored at regular intervals.
The process of wiping off the excess PEG must be performed carefully, by experienced hands. As mentioned in previous reports, while carrying out this final stage, many details pertaining to ship construction were observed. These findings will be reported elsewhere.
The keel is now stored in its tank and may be viewed and studied by professionals and amateurs alike. It waits, together with the remainder of the conserved wood, for the completion of the new museum hall being constructed at the University of Haifa. The building of the hall has been made possible by the generous support of Sir Anthony and Lady Jacobs, of London.
Together with the project director, Elisha Linder, we intend to continue our work. The next step will be the publication of our results, along with the reassembling of the ship and ultimately the construction and launching of a replica.
Acknowledgements. Pinhas Peled, the CMS restorator, has continued to assist in both the planning and practical stages of this project. He has invested endless hours of meticulous and highly professional work, with unflagging enthusiasm. We are grateful to the Evolution laboratory for allowing us the use of their equipment. This enabled us to scientifically control the conservation process. Thanks go to the staff of the maintenance and electrical departments whose willing assistance was given over days, nights and weekends. We would also like to thank Poul Jensen from the Danish National Museum Conservation Laboratories for his valuable advice. He is a both a good friend and a real professional.
Y. Kahanov recives Sir Anthony Jacobs and Maestro Isaac Stern in the Conservation Laboratory. (Photo: E. Linder)