PREPARING HISTORIC WROUGHT IRON FOR PROTECTIVE COATINGS: QUANTITATIVE ASSESSMENT TO PRODUCE EVIDENCE-BASED PROTOCOLS

Painted historical wrought iron commonly occurs outdoors exposed to the prevailing climate. Maintaining protective paint layers is an interventive process that often involves removing existing paint layers and repainting. Whilst prior surface preparation greatly affects the longevity of any paint layer, its impact on the metal surface and paint performance has received limited research within heritage contexts, making their selection anecdotal or driven by manufacturers ’ guidelines. Historic Scotland-funded research at Cardiff University is quantitatively investigating the effect of surface preparation methods on wrought iron corrosion rates prior to paint application. The feasibility of using historic sample material in this research has been investigated and is reported. Testing historic wrought iron samples in quantitative studies of corrosion offers more direct linkage to heritage scenarios thus facilitating interpretation of results and extrapolation to real time heritage contexts. The use of an oxygen consumption technique to quantitatively determine the corrosion rate of five samples of historic wrought iron in controlled conditions of 90 % relative humidity and 20 oC is reported. Results returned corrosion rates indicating a level of reproducibility that, with an error calculation, will allow corroded historic wrought iron to be used for production of test samples to be employed in experiments designed to determine the impact of surface cleaning techniques on the corrosion rate of corroded heritage iron