PEWTER PLATE
From the Punta Restelos shipwreck. Recovered by the Finisterre Project.
Pewter is an alloy of mainly tin with a little amount of copper, antimony, bismuth and traditionaly lead, though it is less used today because of its toxicity. It was commonly used for tableware until the 18th and 19th centuries.
Though severely warped, relatively speaking it was in good condition with a substantial metal core and the original surface. The scratches on the surface may have been caused during or after the shipwreck, or they may be traces of its daily use. The electrolytic reduction revealed all the surface details, like the concentric lines of the bottom.
For more information on this shipwreck and others on the Finisterre coast you can read the Finisterre Project blog at the Institute of Nautical Archaeology.