Conservation Highlights
Freeze-Drying Ship Timbers at the Maryland Archaeological Conservation Lab

Finally ready for drying, timbers from site 31CR314 (La Concorde/Queen Anne's Revenge) make a trip to Maryland for special treatment

Author: Kimberly Kenyon, Head Conservator

Oak plank
Oak plank from the QAR site

Following the devastation wrought by Hurricane Floyd in 1999, it was discovered that several previously unknown ship timbers from La Concorde/Queen Anne’s Revenge had been exposed. The storm caused a massive shift in the overlying protective layer of sediment, revealing the well-preserved wood for the first time. It was clear that the timbers had been buried and effectively sealed off from the harmful effects of hundreds of years of erosion. Since the protective cap of sand had been disturbed, the next step was to remove them from the seabed. Leaving the wood in place would risk damage and loss of invaluable archaeological information about how La Concorde was built. Since we have so little surviving hull, their retrieval was imperative.

Map of planks
Map of planks on site

In November 2000, the Underwater Archaeology Branch undertook an emergency recovery, swiftly mapping and excavating the frames and planks. The frames are thick oak timbers that act together as a ribcage, providing support and internal strength over the length of the hull. The skin of the ship is made up of two layers: one inner layer of oak planking and one outer layer of pine. This outer pine layer is often referred to as sheathing or sacrificial planking and protected the oak from wear and tear during a voyage. The oak is extremely well preserved and just as stout as the day it was felled.

MAC Lab freeze dryer
Loading the timbers into the freeze dryer

The two types of planking were separated by species for conservation. While the pine is still desalinating and currently being prepared to begin its polyethylene glycol (PEG) treatment, the oak recently completed treatment and was finally ready for drying. Research has indicated that the best outcome for waterlogged wood following impregnation with PEG is to freeze-dry it. This entails deep freezing the wood and applying a vacuum to remove the frozen water directly to a gas state in a process called sublimation. At the QAR Lab, we have a 6-foot freeze-dryer capable of treating most of our organic artifacts. However, these timbers well exceeded that capacity, and we needed to find another solution.

The Maryland Archaeological Conservation Lab (MAC Lab) at the Jefferson Patterson Park and Museum regularly conserves artifacts from small to very large scale. The MAC Lab has a 12-foot freeze-dryer and was able to take our planks and finish off their treatment. In early February, we carefully packaged the timbers and drove the five hours north to the MAC Lab. There, conservators Nichole and Arianna were prepared to accept our precious delivery. Over the coming months, the planks will be dried, after which they will return to our lab and be prepared for eventual exhibit!


One of the oak planks ready to be dried. Image by NC Department of Natural and Cultural Resources.

Site plan of the wood as found on the seabed. Image by NC Department of Natural and Cultural Resources.

MAC Lab conservators Nichole and Arianna and QAR conservator Kim loading the timbers into the freeze-dryer. Image by/courtesy of the Maryland Archaeological Conservation Lab. Used with permission.

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