Science and Stone: A video

Friday, Mar 7, 2014

Video by Jeremy Blair

George Scherer, William L. Knapp '47 Professor of Civil Engineering Professor of Civil and Environmental Engineering and the Princeton Institute for the Science and Technology of MaterialsCherished monuments, from the Parthenon to Versailles, are under threat from harsh environmental elements such as pollution and acid rain. Professor George Scherer's Materials Research Group at Princeton is developing a technique that will protect limestone and marble monuments and statuary by coating them with the mineral hydroxyapatite, the same mineral that protects your teeth.

In this video, Scherer talks about how science can protect the precious monuments of the ancient world.


GEORGE SCHERER: I'm George Scherer. I'm a professor of material science in the Department of Civil Engineering. The work of my group is focused on the durability of building materials. So that includes frost damage to concrete, salt damage, as well as protection of stone and monuments and sculpture. We choose the particular conservation topics through consultation with colleagues in the field.

Monuments around the world, like the buildings at Princeton, are made out of all sorts of different types of stone and exposed to quite a broad range of environments. Each type of stone has its own sensitivities. One of the most important materials in monuments and sculpture is calcium carbonate, which is the mineral that constitutes limestone and marble.

The problem with restoring those materials is that there is not a good commercial treatment right now available to do it. And the reason is a chemical incompatibility. And it turns out that the mineral in your teeth, hydroxyapatite, is chemically and structurally compatible with limestone and marble. The virtue of hydroxyapatite is that it's 10,000 times less soluble than marble.

So all we need to do is to deposit a thin coating of the material on the surface of the marble. And it will provide years of protection. This treatment is very practical. Because it's water-based, the ingredients are nontoxic, they're not particularly expensive, and they're easy to apply. At this stage, we're doing a lot of testing in our laboratory to verify the benefits.

And the next step is to do exposure outside. We collaborated with conservation scientists all over the world. We have colleagues at Versailles, for instance, who are applying this treatment to samples of marble that will be exposed to the environment there. Colleagues in Italy are doing extensive tests in Bologna, and also colleagues in Athens.

The project with hydroxyapatite has sprouted all sorts of new research directions. Right now, our enthusiasm is focused on the broader applications of the phosphate technology, expanding from marble and limestone to mortars and concrete and other applications where this chemistry can be very effective. More broadly, this area of art conservation is simply a beautiful application of material science.

In a field where most of the effort has been directed toward healing the symptoms of the problem rather than treating the cause, there are only a few laboratories around the world taking that approach. Our goal here is to persuade people that science is not the enemy, that science can have very important contributions to preserving our environment, preserving our culture. And this is one of the most direct ways in which that can happen.