Synthetic · Antiquity to the 20th century
Historically fatal toxicity
Lead is a well-documented neurotoxin; historical exposure among painters and pigment workers is well documented in the medical literature.
Banned or heavily restricted in most countries for paint and consumer products due to lead toxicity. Not used in modern artists' paint from major manufacturers.
Lead white is mainly basic lead carbonate (the compound of the mineral hydrocerussite) with some neutral lead carbonate. It absorbs almost nothing in the visible range, and its high refractive index in oil makes it scatter light strongly, so it covers well while staying slightly warm and translucent in thin films. Lead also speeds the drying of linseed oil and forms tough, flexible films, which is much of why painters valued it beyond its whiteness.
For most of its history lead white was made by corroding metallic lead with vinegar vapour and carbon dioxide. In the 'stack' or Dutch process, coils of lead sat over vinegar in pots buried in fermenting dung or tan bark, which supplied warmth and carbon dioxide; over weeks a white crust formed and was scraped, washed and ground. The work was notoriously dangerous for the people who did it. Studies of lead isotopes in Dutch paintings show the source of the metal changing in the 1640s as trade and war disrupted supply.
Lead white is lightfast but reactive. Hydrogen sulfide from polluted air or neighbouring sulfide pigments can turn it into black lead sulfide, a problem mainly in unprotected watercolour, drawing and wall painting. In oil, the lead reacts with fatty acids from the binder to form lead soaps; these can aggregate into small lumps that push up through the surface as protrusions, and soap formation is thought to contribute to oil paint becoming more transparent with age, so earlier changes of composition can start to show through.
Lead absorbs X-rays strongly, so lead white dominates an X-radiograph, which is why X-rays reveal a painting's underlying design. XRF detects lead readily, and infrared and Raman spectroscopy distinguish the carbonates, while cross-sections show soap aggregates. Lead isotope ratios, measured on tiny samples, can indicate where and when the metal was sourced, supporting dating and attribution.
Zinc white and then titanium white replaced it through the 20th century. Titanium dioxide is far more opaque and brighter, is non-toxic and does not darken with sulfur, but it lacks lead white's warmth, its fast, flexible drying and its particular handling. Zinc white is cooler and more transparent but can make brittle oil films. Lead white is now restricted almost everywhere and survives only in specialist use.
FactStrong evidence
Lead white is mainly basic lead carbonate with some lead carbonate; it is lightfast but converts to black lead sulfide in the presence of hydrogen sulfide.
Source: Lead white — ColourLex pigment page; The National Gallery, London (conservation and pigment research)
FactStrong evidence
Lead soaps form when lead from pigments reacts with fatty acids from the oil binder, and can accumulate into protrusions that damage a painting.
Source: ToF-SIMS Parallel Imaging MS/MS of Lead Soaps in Embedded Paint Cross Sections
FactStrong evidence
Lead isotope ratios in lead white from 77 Dutch paintings dated 1588–1700 shift during the 1640s, consistent with a change in lead supply, which can help date paintings.
Caveat: Specific to Dutch paintings of that century; other regions and periods have their own signatures.
Source: Time-dependent variation of lead isotopes of lead white in 17th century Dutch paintings