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| White lead | |
|---|---|
| Other names | basic lead carbonate |
| Identifiers | |
| CAS number | 1319-46-6 |
| Properties | |
| Molecular formula | (PbCO3)2·Pb(OH)2 |
| Molar mass | 775.633 g/mol |
| Appearance | white powder |
| Hazards | |
| Main hazards | lead poisoning |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references |
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White lead is the chemical compound (PbCO3)2·Pb(OH)2.1 It was formerly used as an ingredient for lead paint and a cosmetic called Venetian Ceruse, because its opaque quality made it a good pigment. However, it tended to cause lead poisoning, and its use has been banned in most countries.
White lead has been the principal white of classical European oil painting.2 There have been claims that it is partly responsible for darkening of old paintings over time, reacting with trace amounts of hydrogen sulfide in the air to produce black lead sulfide. Other authorities dispute this; the most traditional view is that impermanent pigments and dirty varnish (which is often cleanable) are more likely responsible for darkening. In any event, white lead has been mostly supplanted in artistic use by titanium white, which is structurally weaker than white lead. White lead is less used by today's painters, not because of its toxicity directly (since painters generally know not to engage in the behaviors that make lead white dangerous); but simply because its toxicity in other contexts has led to trade restrictions that make lead white difficult for artists to obtain in sufficient quantities.
Historically, white lead was produced by the Dutch process. This involved casting metallic lead as thin buckles. These were corroded with acid in the presence of carbon dioxide. Next they were placed in pots with a little vinegar (containing acetic acid). These were stacked up and left for six to fourteen weeks, by which time the blue-grey lead had corroded to white lead. The pots were then taken to a separating table where scraping and pounding removed the white lead from the buckles. The powder was then dried and packed for shipment.3
White lead occurs naturally as a mineral, in which context it is known as hydrocerussite1
Other synonyms (as an art pigment)
from 2
ceruse, flake white, silver white, slate white, Berlin white, Cremnitz / Kremnitz white, Crems / Krems white, Nottingham white, Vienna white
References
- ^ a b Inorganic Chemistry,Egon Wiberg, Arnold Frederick Holleman Elsevier 2001 ISBN 0123526515
- ^ a b "Stack Process White Lead (Old Dutch Method)". Commercial supplier, offering original pigments to the conservation and reproduction markets
- ^ Lead411.org based on Warren, Christian. 'Toxic Purity: The progressive era origins of America’s lead paint poisoning epidemic'. Business History Review. Winter 1999, Vol. 73(4)
