The use of an electric field for the removal of alum from treated wooden objects

In this paper the removal of sulfate and aluminum ions from waterlogged alum treated wood with the use of an applied electric field is in focus. Removal of alum is seen as the first step towards re-conservation of the wood with e.g. PEG. Alum treated wood samples from the Hjortspring finds (app. 350 BC) was used in this investigation and a total of six experiments are presented here. An electric DC field was applied across the wood for 4-20 days. A constant current of 1-5 mA was applied and the corresponding voltage drop initially low, often below 10 V. At the end of the experiments sulfate has moved as expected towards the positively charged electrode (anode) and after 20 days only 10% of the sulfate was left in the wood. The majority of the sulfate was removed with the use of the electric field. It was shown that it is possible to apply the electric field and remove sulfate in both experiments with and without presoaking. Aluminum tended to be removed more slowly and even after 20 days only minor amounts of aluminum was removed from the wood, The power consumption was low, only 1.6 Wh after 20 days. An increase in ph near the anode was found in some of the experiments. The reason is not obvious and further experiments are needed to evaluate the reason for this. Total removal of alum was not obtained in the experiments reported here, but the high conductivity and the transport of the measured ions due to the electric field indicates that an applied electric field as a method for removal of alum and other unwanted ions from treated objects should be further investigated. Research is ongoing and distribution of potassium after treatment will be measured in the near future.