Dr Joanna Dowle (Senior Advisor at the Environmental Protection Authority) outlines the long and varied history of how we’ve used lead – despite its toxicity.
This is an excerpt from the EPA’s Science at work series of science communication stories.
Lead was one of the first metals discovered and used by humans, with evidence of its use dating back to 6,500 BCE.
Lead is a normal part of the earth’s crust, usually combined with other elements such as oxygen and sulphur. Lead metal is easily obtained by roasting the lead ore galena (natural mineral form of lead) in hot air, leaving metal that is soft, easily worked, and corrosion resistant.
Unfortunately, it’s also highly toxic and no amount of lead is considered safe. It accumulates in the body and can lead to permanent damage of the brain and nervous system, can lead to anaemia and kidney damage, and can impair fertility or even cause death.
Lead is also toxic to plants, animals, and even micro-organisms.
Civilisations throughout the ages have found many uses for lead – from plumbing to pottery glazes, and from stunning stained glass to soldering electronics in the more modern era.
Toxic beauty
Pigments containing lead, especially white lead, have been used in cosmetics since ancient times.
This seems horrifying given what we now know about its toxicity, but white lead make-up was used extensively in various cultures to achieve a highly prized pale complexion. Other lead pigments were also used in various cosmetics, including lipstick, rouge, and eyeliner.
Even though lead toxicity has been known for a long time – the first written account of lead poisoning dates to the 2nd Century BCE – lead-based creams and makeups made their way onto the dressing tables of women well into the 19th and early 20th centuries.
Recipe for disaster?
Lead white is the synthetic lead carbonate hydroxide (or basic lead carbonate) and it is one of the oldest synthetic pigments. It has been made since antiquity using a process later named the ‘stack’ or ‘Dutch’ process.
In this process, thin sheets of lead were placed in jars over acetic acid (that is, vinegar) vapours in the presence of moisture and carbon dioxide. This was usually done by surrounding the jars in fermenting matter such as horse manure or waste grape skins, which give off the required carbon dioxide and moisture, and also provide a constant source of heat.
The action of the acetic acid on the thin metal causes a chemical reaction, leaving a white deposit of basic lead carbonate. The white 'mould', as it’s often called, is scraped off, dried, ground into a powder and sold as lead white, or flake white.
Continue reading the story: A story of lead | EPA
