We present analyses of lead glazes from dishes and storage bowl from six Renaissance (1536 to 1660 CE) sites in southern Denmark and northern Germany. All are high-lead silicates, ranging from 55 wt% to 75 wt% PbO, with only silica and alumina routinely exceeding c 1 wt%. The underlying bodies are ferruginous clays with 15 to 20 wt% Al2O3 and <10 wt% Fe2O3.
Here, we discuss the relationship between the PbO content in the glaze with the amount of lead entering acidic foodstuffs stored or served in these vessels. The experiments used 4 wt% acetic acid, similar to common foodstuffs preserved with vinegar such as pickles. This concentration is high enough to be effective in preserving food, while low enough to taste good. It also approximates official test methods for the release of Pb for glass hollowware in contact with food according to ISO 7086-1.
We found a strong exponential correlation between lead leaching and lead oxide content in the glaze, reaching toxic levels in the leachate solution after short periods of exposure (less than 1 day) for PbO contents above c 70 wt% PbO. Our research shows that widely distributed lead-glazed ceramics had the potential of being a main source of Pb in human bodies. How the pottery was actually used, in combination with kitchen wares fashioned from other materials, might explain why lead-glazed ceramics might not have had quite the poisonous consequences the etching experiments suggest.