The application of organic coatings in conservation of archaeological objects excavated from the sea

Protection of maritime cultural heritage is the mission of the National Maritime Museum (NMM) in Gdansk. This includes preservation of historical, cultural objects related to boat building, shipbuilding, sailing, military science, maritime education etc. Many archaeological objects, made from metal, wood and other organic materials and excavated from a wet environment, are kept at the NMM in Gdansk. In order to prevent the objects from any further degradation after the initial conservation process, different approaches are used including application of coatings, wax, paraffin wax and/or addition of different inhibitors. Due to various limitations (costs, human resources) conservators have been evaluating the performance of the coatings based on visible changes (corrosion signs) to decide when reapplication of the coating is necessary. In most cases the visible changes are indicators of coating damage and are non-reversible in character. Therefore there is a great need to find a method that will allow assessment of the performance of the coating in a relatively short time and efficient way. Electrochemical techniques such as measurement of DC resistance, Electrochemical Impedance Spectroscopy or Electrochemical Noise Measurement offer a way of achieving this. Each produces a number which is a measure of the ability of the particular coatings/inhibitor to protect effectively. In this paper the authors take as examples four coatings used to protect metal objects from particular shipwrecks found in Baltic area. Results are presented of some preliminary work conducted attempting to assess (rank) these four coatings on steel and copper using the DC resistance method. It is anticipated that this work will become one potential strand of a new development plan for better maintenance of archaeological objects.