The InternationalJournal of Nautical Archaeology (1999) 28.2:164-173 Article No. ijna.1999.0191 Technical Communication Monitoring the effect of sacrificial anodes on the large iron artefacts on the Duart Point wreck, 1997 David Gregory National Museum of Denmark, Centre for Maritime Archaeology, Havnevej 7, Postbox 317, DK-4000 Roskilde, Denmark The in situ measurement of electrochemical parameters such as surface pH and cor- rosion potential, Ecorr, of corroding metal objects on submerged wreck sites has a relatively recent history. Undoubted pioneers in this research are Dr Ian MacLeod and his colleagues of the West- ern Australian Museum. Their work spans over two decades and during this time they have shown that the routine recording of on-site measurements has been an invalu- able tool in understanding the corrosion mechanisms and modes of deterioration of metals on marine archaeological sites. Fur- ther, they have shown that with the aid of such information it is possible to stabilize and start the conservation process of iron artefacts on the seabed with sacrificial anodes, thereby significantly reducing the time and cost of subsequent conservation in the laboratory (North, 1976, 1982; MacLeod, 1987, 1989, 1995, 1996). The benefits of attaching sacrificial anodes to artefacts to start the conser- vation process in situ have been discussed by MacLeod (1987: 51). A sacrificial anode normally comprises a metal such as a zinc or aluminium alloy, electrically connected, for example by copper cable, to the arte- fact which is a less reactive metal, such as iron. The iron artefact gains protection as the electroris released from the corroding 1057-2414/99/020164+ 10 $30.00/0 anode flow through the copper wire into the artefact; that is to say, the artefact is the cathode of the corrosion cell while the seawater completes the circuit. This effec- tively lowers the corrosion potential and hence the corrosion rate. Furthermore, as electrons flow into the artefact they will tend to cause a reduction in the acidity levels of the solution trapped between the concretion/metal artefact interface as hydrogen is evolved. The effective change in polarity of the artefact will assist the removal of chloride ions. The fact that removal of chlorides from artefacts is effected while still in situ will mean that less time is required for conservation in the laboratory. In 1994 Dr MacLeod visited the Duart Point site and took measurements on five of the cannon and the anchor, leading to his recommendations for future in situ conservation (1995: 57). His results are tabulated in Table 1. In 1996, based on his findings, a series of aluminium anodes were attached to the cannon and anchor. His recommendations were that cannon 4 and 5 were not in imminent danger of collapse. However, cannon 1 and 3 and the anchor needed urgent attention. The anodes consisted of scrap aluminium smelted into ingots which were attached to clamps by means of a © 1999 The Nautical Archaeology Society