Of the handful of 16th century basket-hilted swords in existence the Mary Rose sword is arguably one of the most important because it can be dated precisely as the sinking of the ship in 1545 is well documented. This sword, recovered in September 1982 by a diver working in the silt under the ship’s side as part of the preparations for the lift later that year, is unique amongst artefacts recovered as every other metal edged weapon was almost completely destroyed by the sea bed environment leaving only the wooden parts and just a few fragments of metal trapped within concretions. It had apparently fallen through a gun port as the ship sank in 1545 and then was buried beneath the hull as it settled into the sea bed.
When found the sword was heavily concreted. After initial cleaning the sword was found to be in remarkable condition with small portions of the blade and one element of the basket hilt missing and the remainder crushed by the weight of the ship as it settled to the sea bed. The sword is a composite object: the handle is wood, either poplar or alder; the blade is made of iron with steel cutting edges and the basket hilt is made from quarter inch iron rods hammer welded together. Even after 437 years in the sea the sword is still wonderfully balanced and the edge of the blade near the hilt is sharp enough to cut.
Initial chloride removal was completed in November 2004 following 18 months in a sodium sesquicarbonate solution. Following this the sword was placed in wet storage until the next process could begin. Electrolysis was then started in order to reduce the chloride levels even further. The next stage was to dehydrate the sword using a solution of industrial methylated spirits before finally treating the wooden hilt. After all these many years of conservation it has been possible to display the sword in the museum for the first time.This display was officially opened in July 2007.
Obviously with all the hard work that has gone into restoring the sword, the Trust needed to ensure that it would be preserved for a long time to come. They contacted Munters, the humidity experts, for a solution.
The sword is displayed in its own sealed case and the humidity levels and temperature are strictly controlled using a Munters desiccant dehumidifier. The relative humidity levels are maintained at 35% RH, which is the optimum level for preserving metals. The Munters dehumidification unit is placed outside the case for aesthetic reasons and the dry air is vented in. The benefits of using desiccant dehumidification for preservation purposes are that the sword will not experience any corrosion, no condensation will form on it and as the ambient moisture is removed creating the exact conditions required for preserving this specific type of metal.
The Munters principle:
The system is designed around the desiccant drying rotor, which is the moisture absorbing component at the heart of the dehumidifier. Air to be dehumidified (in the display case) is drawn through the rotor, where moisture is absorbed and the resulting dry air is delivered back to the case. Simultaneously a separate air flow is heated and drawn through the remaining sector of the rotor. This air removes the moisture from the rotor and is discharged to the atmosphere.
As well as the 500 year old sword, Munters desiccant dehumidification systems are also protecting the pewter case, the swivel gun and the drying room.
