The greatest of the whites, and certainly the cruellest, is made of lead. It is hard to imagine a history of art without this dense ‘silver’ white.

Lead may have been liberated from its ores as early as 5000 years ago as there is extensive evidence of lead smelting in Anatolia from around 2300 BC.

The manufacture of white lead from the metal is remarkable partly for its methodical process and partly for its longevity: much the same technique was used in Ancient Rome and most probably employed centuries earlier in Egypt, was still in use in the 19th century.

White lead is basic lead carbonate. It is made via an intermediate substance, the salt lead acetate, formed when acetic acid, as vinegar, reacts with lead metal.

The Dutch ‘stack’ process of the 19th century involved using clay pots divided into two sections – one for the lead and the other for vinegar. Several dozen of these pots were lined up, then covered with large quantities of warm manure straight from the farm to produce not only the heat to evaporate the acid but also the carbon dioxide to transform the substance from lead acetate to basic lead carbonate. The room was sealed, and left closed for ninety days.

It really amounts to nothing more than the corrosion of the metal by acids but this alchemical magic, the dirt and the smells metamorphosing into the purest white, forms as akes on the grey metal. For hundreds of years it has been the most important paint for artists.

In the manufacture process displayed for the exhibition, the chemical process has been replicated by a modern method that, luckily for us, dispenses with the use of manure!

The lead coils have been placed in jars that sit within open dishes of high-strength vinegar. The introduction of a warm yeast and sugar solution provides both heat and the creation of carbon dioxide.

You can see within the display how the lead pigment develops over intervening weeks. The initial reaction is rapid but the full convesion of all the lead to ake white takes three months. You can easily see why the pigment got its name Flake White.! After complete formation, the pigment is washed to remove any soluble impuri- ties, dried and ground down to a ne powder.

It had one major defect: lead is so poisonous that prolonged exposure would kill you. This was not such an issue for artists whose contact through paint was fairly limited, but for workers in lead white factories the symptoms of poisoning included headaches, irritability, memory issues, abdominal pain and even- tually death.

Not until the 19th century was white lead superseded by safer synthetic whites. First, Zinc White became a competitor and then in the 20th century the introduction of Titanium White almost completely replaced leads’ use.

Still used by artists, its qualities in oil paint cannot be underestimated. A dense white with excellent brushing qualities and rapid drying, it mixes with other colours without overpowering them.