PROVIDENCE -- A Brown University chemistry professor testified here yesterday that if lead paint is covered with just one coat of non-lead paint, the lead could remain intact on a house for centuries.
Prof. Joseph Stein, who has been teaching and doing research at Brown since 1966, told the jury lead paint doesn't dry in the sense that some component of the paint evaporates. When lead paint sets, a chemical reaction actually takes place that can continue for decades and make the paint surface increasingly stable.
Stein said he spent years doing research in oils and fats but now concentrates on teaching chemistry to freshmen and sophomores. Yesterday, it seemed he had turned Courtroom 11 into a freshman chemistry class.
Using a large tablet and a felt-tipped pen, Stein lectured on what lead paint is, what makes it durable and what causes it to deteriorate. Lawyers crowded alongside the jury box and watched him sketch interlocking molecules that looked like strings of spaghetti.
Stein spoke of concepts such as how van der Waals' forces cause lead to adhere to walls, polymerization accounts for its stability and hydrolysis is one of lead paint's downfalls.
He was the second witness presented by eight companies that once made or marketed the lead paints two generations ago that continue to poison thousands of Rhode Island children each year.
Atty. Gen. Sheldon Whitehouse is suing the companies, arguing that their paints create a public nuisance. The paint companies insist their paints are safe if properly maintained.
Stein said lead-based paints were usually made with linseed oil that contained particles of white lead and other pigments.
Linseed oil comes from flax seeds, he said, and is similar to other vegetable oils. A big difference, he said, is that when it is exposed to air it polymerizes: a chemical reaction takes place among the oil molecules and they harden into an almost natural plastic.
The molecules look like spaghetti strands and like spaghetti when it's just cooked, they are usually flexible and slide past each other, Stein said. But when the chemical reaction takes place, the strands interlock and become solid, with the lead particles fixed among them.
"It's like a concrete sidewalk. The pebbles would be the pigment particles," Stein said.
He said the initial chemical reactions can take days or a week. But the oil keeps forming cross links for as much as two decades.
Defense lawyer Donald Scott asked how the paint adhered to smooth surfaces.
Most surfaces aren't as smooth as they look, Stein said. The paint interlocks mechanically to the surface like pieces of a puzzle.
There also are electrical attractions called van der Waals' forces, he said. They explain how paint adheres to glass.
Ultraviolet light, the component of sunlight that causes sunburns, can cause lead to break down and become chalky by triggering what Stein called "a free radical reaction."
But he said just one coat of non-lead paint would prevent that oxidation process from occurring.
Water leaks also could trigger a breakdown known as hydrolysis, Stein said.
But if the lead paint were covered with one coat of non-lead paint and protected from water, the causes of damage would be minimized and the paint would have enormous stability.
"Left to its own devices, we're talking centuries," Stein said.
