Please note that lead is a toxic element linked to serious medical conditions. If handling lead please do so with the utmost care and use appropriate personal protective equipment as advised by the Health and Safety Executive website.
Until the twentieth century's discovery of titanium white, lead or 'flake' white was THE white pigment used by both artists and architectural painters and decorators. Much was made here in the United Kingdom. It is a pigment that has always required great care in the making and has been regulated since 1883. Pliny famously first recorded the potentially deadly effects of lead exposure. Although purchasing and supplying lead white is restricted today, it remains renowned for its covering power and handling.
The easiest way to make lead white today remains the stack process. This was used extensively during the nineteenth century and can take between two and four months to complete, depending upon ambient temperatures.
In the nineteenth century lead stacks could be built up to twenty-four feet high, but we have been making more easily portable stacks of approximately half a foot high. First the sheets of lead need to be wiped over with acetic acid to remove any grease or dirt that could contaminate the pigment. Then these can be rolled up into loose coils and placed into terracotta or ceramic pots so that they balance above a reservoir filled with acetic acid. Do ensure that the lead does not come into contact with the acid.
The pots can then be sunk into a container with enough fresh horse manure to surround but not submerge them and the container sealed tightly. The decomposing horse manure should provide enough heat and carbon dioxide to vaporise the acid. As the surface of the lead coils oxidises, wintery flakes of lead carbonate form. Should there be any copper inclusions a gentle turquoise blush may appear in parts, this copper carbonate can be extracted later.
After two to four months the lead white flakes can be carefully brushed from the coils into a suitable container filled with clean water. An appropriate respirator in working order is essential for this stage as lead dust is extremely toxic and must not be breathed in. Raking the flakes to and fro in the water allows the lead particulates to sink to the bottom, separating out any impurities. The water can then be drained off and disposed of in accordance with current government regulations, while the lead white sediment can be left to dry.
Once the lead white flakes have thoroughly dried out they can be ground into a useable pigment. Again using an appropriate respirator, in good repair, at all times. This astonishingly pure white pigment can then be mixed with a cold pressed linseed oil to create a bright lead white paint.