Lead White was being produced during the 4th century BC; the process is described by Pliny the Elder the Roman philosopher.
The traditional method of making the pigment was called the stack process. Thousands of earthenware pots containing vinegar and lead were embedded in a layer of either tan bark or cow dung.
The pots were designed so that the vinegar and lead were in separate compartments, but the lead was in contact with the vapor of the vinegar. The lead was usually coiled into a spiral and placed on a ledge inside the pot. The pot was loosely covered with a grid of lead, which allowed the carbon dioxide formed by the fermentation of the tan bark or the dung to circulate in the pot.
Each layer of pots was covered by a new layer of tan, then another layer of pots. The heat created by the fermentation, acid vapour and carbon dioxide within the stack did their work.
Within a month the lead coils were covered with a crust of white lead, which was separated from the lead, washed and ground for pigment.
Medieval texts warned of the danger of “apoplexy, epilepsy, and paralysis” from working with lead white.[
To protect the painters’ health, France had already passed in 1909 a law banning the use of paints containing lead
As of 2018, there are an estimated 37 million homes and apartments with lead paint in the United States.
Imagine if you can, the use of vermilion paint coloured by pigments made from a mercury compound to paint your bathroom, or perhaps choosing a green paint containing arsenic to finish the fence painting! Both scenarios are unimaginable today yet were commonplace a century ago.
Paint manufacturing has certainly come a long way since then, with toxic substances such as mercury, arsenic and more recently, lead, no longer acceptable ingredients in the paint chemist’s repertoire.
These restrictions are just the tip of the iceberg. Recent attention has focused on the effect of volatile organic compound (VOC) emissions on our environment.
It is estimated by the Paint Quality Institute that 10% of the ozone depleting substances in the urban United States are a direct result of VOC emissions from surface coatings, including mainly standard household paints.
Paints are manufactured using a wide range of organic and inorganic materials. They can contain components that can impact adversely on the environment at different stages of the product’s lifecycle releasing solvents and toxic substances during production, application, the service life of the coating and disposal.
In response to growing concerns over VOC emissions, the Environmental Choice programme focuses on the need to reduce these emissions. Solventborne paints release significantly more VOCs per litre than waterborne paints, spurring chemists to develop waterborne replacements for solvent borne products.
Trim, joinery and wet areas were traditionally no-go areas for waterborne paints due to a tendency to soften under prolonged exposure to moisture and poor block resistance (the ability of a paint to not stick to itself when two painted surfaces come into contact) but modern water-based enamels have overcome these challenges.
Low VOC paints are now available, and thankfully the emphasis has moved towards cleaner, greener paints and coatings.
Bright colours no longer must harm the environment, meaning we have truly moved out of the dark ages!