A giant freezer is the latest piece of technology being used in conservation work by archaeologists in York.

The freeze-drying unit will be used to preserve waterlogged archaeological wood, such as medieval timbers recently rescued during construction of the new Layerthorpe Bridge.

The equipment will be used to remove water from fragile organic materials without the shrinkage normally found during ordinary drying.

The York Archaeological Wood Centre, part of the conservation department of the York Archaeological Trust, says it has a vacuum chamber capable of holding the equivalent of 20 telegraph poles.

The wood is frozen down to -20 degrees Centigrade before a powerful vacuum is applied to draw the ice off as water vapour.

The remains of a Roman boat and a medieval boat, found in South Wales, will also be put through the process shortly before being returned to museums in Wales.

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