The present paper studies the corrosion mechanisms of blue enamel powder samples, immersed in water, reproduced according to historic recipes from an 18th-century manuscript. The pH increase of the electrolyte reveals an ionic exchange between the alkaline ions of the glass and the hydrogen-bearing ions of the water. With the lixiviation of the alkaline components, cobalt is influenced by other neighbouring ions, leading to a change of enamel colour. In two high-lead samples, hydrated lead white and Co2+/Co3+ spinels were identified, which explains their complete colour fade. The influence of Pb2+ ions may increase in detriment of the Co2+ ions.
- Stained glass