massicot

Massicot is lead monoxide (PbO), a pale yellow powder produced by heating white lead (lead carbonate) to approximately 300°C. The word entered English from Old French massicot, which may derive from Italian marzacotto or Arabic martak (مرتك), a term for lead oxide used in ceramic glazes. The etymology is uncertain, but the Arabic connection is supported by the pigment's long history in Islamic pottery.

The production required precise temperature control. Below 300°C, the lead carbonate did not fully convert. Above 500°C, it transformed into minium—red lead, a completely different pigment and color. The narrow temperature window made massicot difficult to produce consistently. Medieval recipes described the process in terms of color change: heat until it turns 'the color of gold,' stop before it turns 'the color of fire.'

Massicot appeared in European panel paintings from the 1300s onward, often in combination with other yellows. Conservators have identified it in works by Botticelli, Mantegna, and Bellini. It was cheaper than orpiment and less toxic (though still a lead compound), making it the practical painter's yellow. But it had a weakness: in oil, massicot became semi-transparent over decades, causing yellow passages to fade.

Lead-based pigments were banned in most countries by the late 20th century. Massicot is no longer produced commercially. But lead monoxide persists in industrial applications—it is used in lead-acid batteries, ceramic glazes, and glass production. The yellow pigment that medieval painters coaxed from a narrow temperature window is now manufactured by the ton for purposes its makers never imagined.