Analysis of the corrosion products on lead artefacts recovered from historic shipwreck sites not only identifies the nature of the patina but it also provides an insight into the processes of decay across the site. From a comparison of the mineralogy of the lead corrosion products and their thermodynamic stability constants, it is possible to obtain a corrosion map of the areas from which the artefacts were recovered. The corrosion maps correlate with the levels of extractable chloride obtained from desalination data during treatment of artefacts. This data has general applicability regardless of the historical period pertaining to the wreck since lead is nearly always present on wreck sites. Corrosion simulation experiments in normal sea water provide an insight into the competing kinetic and thermodynamic forces that control the rate of deterioration of lead. The electrochemical data assists in the interpretation of the differences in patina.