A late Bronze Age sickle was found at the Shinewater Park Sacred Water Site, Sussex, England in 1995 as we reported earlier. The following is an abbreviated extract from the superlative report about the conservation undertaken on the sickle by the specialist form the British Museum, Ann Brysbaert. A thoroughly researched conservation plan was required in order to meet the display conditions of the receiving museum and to meet the high standards required by the specialists involved in the treatment of this unique sickle.
The site was discovered during the excavation of a lake which forms part of a new community park being developed by Eastbourne Borough Council. The object was found in a peat environment and was block lifted from site in this soil.
Some of the remains found on site include post alignments and other wooden structures, a skeleton of a child, antler artefacts and several copper alloy objects, including the sickle. The latter finds and the post alignments have suggested to some a comparison with the site of Flag Fen in Cambridgeshire, according to M. Taylor, an independent wood specialist (personal communication). Together with the other copper alloy objects, the sickle was recorded to have lain horizontally in the acidic peat. The pottery from the site gives a date around 800-600 BC, which is Late Bronze Age or Early Iron Age.
Object description and technology
The object could be partially described before it was taken out of its surrounding peat, and more details became available after lifting and cleaning procedures were carried out.
The sickle consisted of two main materials. The metal of the blade was considered to be a copper alloy and the wood of the handle was identified through a sample as Field Maple (sample taken and identified by M. Taylor).
The amazing Bronze Age Sickle itself
It is not entirely clear how the slightly curvy metal blade and hollow socket with two rivet holes would have been shaped. It may have been cast in an open, single piece mould. Ridges ran along the blade on both sides.
The grain of the wooden handle ran along its length. The end of the handle formed a clearly cut curved part, nicely rounded and worked. This curve probably stopped the hand of the user from sliding off the instrument during usage. This curved part also gave an idea of how the object could have been used: a straight cutting movement was made towards the body of the user. A small hole went through the thickness of the handle about 2.5 cm below the metal socket. The hole seemed to be deliberately made because of its square section. Taylor suggested that if it was purposely made, a rope could have been put through it to enable the owner to carry the sickle on his belt. But the option that the hole was the result of animal activity during burial was not excluded.
The connection between the wooden handle and the metal socket was achieved by the use of two rivets. However, since the diameter of the wood was hardly smaller than the diameter of the metal socket, the wood might have been slightly cut at the socket end in order to fit in the metal piece as an extra way of fitting both parts together tightly. The wood obviously had also swollen because it was buried and became waterlogged.
Conserving the Sickle
Xantopren L was chosen to be the best material for the moulding process because it met all pre-set requirements. The process of moulding was carried out as follows:
- all holes and undercuts were filled with wet acid free tissue to prevent the moulding material from creeping in the wood
- since the metal was much heavier, it had to be suspended onto fine nylon thread to stop it from disappearing in the moulding material when the first half was made.
Treatment was carried out as follows: a solution of water and industrial methylated spirits (IMS) was made up to gradually replace all the water in the object. The percentage of the IMS went up over a period of time until 100% IMS was reached. This solution was then replaced by ether, in which the object was immersed. After 24 hours, it was taken out of the ether and allowed to air dry in a closed fume cupboard. Initially all went well, but after one hour cross-grained cracks started to appear. Fortunately, these all closed up when the object was placed in a normal environment again. A few smaller cracks, however, remained visible at the curved end of the handle, but they were very small.
During further investigation of the metal under high magnification (65x), striations on one side of the blade were visible and were possible signs of use wear. Some corrosion deposits were removed mechanically. Most of the surface was seriously etched and little was left of the “original surface.” The etched areas were not touched during the investigative cleaning process.
Since the future museum environment was not known, the blade was stabilised against further corrosion by brushing on a solution of 3% benzotriazole (BTA) in IMS. Brushing was chosen, in order to keep the rivet holes with the wood uncontaminated. Protective and consolidative layers of Incralac, containing some BTA, finished off the metal.
Conclusions of Ann Brysbaert, the Conservationist
The first aim of the project was to adopt a conservation process that would render the object stable and presentable. A second aim was to learn about the conservation, investigation and analysis of composite and waterlogged objects. A last one was to experience how to work and function in the framework of an ongoing project, involving other conservators, find specialists and experts on different materials. All aims were met and from that perspective, the conservation project was successful.
The following recommendations were made for safeguarding the object in the future:
- light levels should not exceed 50 lux to prevent damage to the wood
- temperatures of 18-20° C are ideal and should be kept stable at all times
- the relative humidity (RH) should be kept stable. This is very important because of the composite nature of the object. Copper alloys and wood require different levels of RH when they are separate. Since this is not possible here, a compromise RH of between 25% and 46% should be set (Erhardt & Mecklenberg 1994). Below 25%, the wood would suffer from being stored too dry and would crack (a potential danger for the sickle because cracks appeared already earlier during the treatment but fortunately closed again). Above 46% copper alloy is prone to active corrosion.
The full report can be viewed at the Journal of Conservation & Museum Studies website.
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