The theory of electrochemical corrosion is described and the need to monitor corrosion potentials of iron artifacts still on-site is stressed. In this way unintentional damage to artifacts during excavation and recovery can be minimized. Sacrificial anodes can be used to conserve historic iron artifacts on the seabed. Scrap aluminum was used to protect an anchor from the wreck of HMS <i>Sirius</i> (1790), Australia, and on a larger scale zinc anodes are being used with the iron steamship <i>Xantho</i>. The problems of deconcreting fragile cast iron and wrought iron from marine sites has been resolved using liquid nitrogen (-196 C). Small historical artifacts are immersed for five to ten minutes and the overlying concretion easily removed. Large artifacts may also be treated: a cannon from the <i>Trial</i> (1622), too large for immersion, had liquid nitrogen poured onto its concreted surface. The concretion disbonded from the cannon and could be carefully prized away. A well-preserved graphitized surface remained.