Urlakning av järn ur arkeologiskt trä med dietylentriaminpentaättiksyra (DTPA): undersökning av koncentrationens påverkan på extraktionstakten

Abstract

The accumulation of iron in waterlogged archaeological wood during burial and its later implications for conservation has been extensively researched in recent years. Methods utilizing high performance iron chelators for the dissolution and extraction of iron have been studied and diethylene triamine pentaacetic acid (DTPA) has proved to be effective in accomplishing this. This study aims to further explore extraction treatments with DTPA and to provide a bridge for the implementation of research into conservation practice. The problem is approached from the perspective of the conservator: how the treatment can be optimized to achieve the aims minimal intervention and maximum benefit as well as time and resource efficiency. The study has experimentally investigated at what levels of concentration of DTPA was most effective at dissolving and extracting iron. The experiment was carried out on wet untreated oak samples from the newly excavated Skaftö Shipwreck (late mediaeval) and on previously PEG-impregnated dry oak from the warship Vasa (1628). After a month of extraction the samples and solutions were analysed. Iron distribution depths before and after treatment were scanned using XRF. The amount of iron extracted in the DTPA-solutions and the remaining iron content in the samples after treatment were analysed with atomic absorption spectrometry. The results were conclusive: the concentration did not affect the effectiveness of the treatment. It appears as it is only effective to increase the concentration of DTPA to a certain level. After this level the extraction rate levels out and the reaction rate appears to become surface rather than diffusion controlled. The extraction of iron with DTPA was equally effective on both materials in this study.