Pearly perfection

June 19, 2013
Pearly perfection
Developing a ratchet-like surface could explain how pearls grow into such perfect spheres, scientists have found. Credit: iStockphoto/Thinkstock

The mystery of how pearls form into the most perfectly spherical large objects in nature may have an unlikely explanation, scientists are proposing in a new study. It appears in ACS' journal Langmuir, named for 1932 Nobel Laureate Irving Langmuir.

Julyan Cartwright, Antonio G. Checa and Marthe Rousseau point out that the most flawless and highly prized pearls have perhaps the most perfectly spherical, or ball-like, shape among all the objects in nature that are visible without a microscope. Pearls develop as nacre (mother of pearl) and other liquids accumulate around grains of sand or other foreign objects inside certain and other shellfish. But how do pearls grow into such perfect spheres?

Pearly perfection

The answer, they say, may be relatively simple—with developing pearls having a saw-toothed, or ratchet-like, surface. That texture generates forces that make the pearl turn inside the oyster's tissues in response to movements in the environment. The result is a spherical build-up of nacre and other textures. Rotating are a perhaps unique example of a natural ratchet, the scientists say.

Explore further: Fraud with cultured pearls can be detected

More information: Cartwright, J. et al. Pearls Are Self-Organized Natural Ratchets, Langmuir. DOI: 10.1021/la4014202

Pearls, the most flawless and highly prized of them, are perhaps the most perfectly spherical macroscopic bodies in the biological world. How are they so round? Why are other pearls solids of revolution (off-round, drop, ringed pearl), and yet others have no symmetry (baroque pearls)? We observe that with a spherical pearl the growth fronts of nacre are spirals and target patterns distributed across its surface, and that this is true for a baroque pearl, too, but that in pearls with rotational symmetry spirals and target patterns are found only in the vicinity of the poles; elsewhere the growth fronts are arrayed in ratchet fashion around the equator. We argue that pearl rotation is a self-organized phenomenon caused and sustained by physical forces from the growth fronts, and that rotating pearls are an example—perhaps unique—of a natural ratchet.

Related Stories

Fraud with cultured pearls can be detected

July 15, 2008

Scientists at the Johannes Gutenberg University Mainz (Germany) advise buyers of cultured pearls to be more vigilant. "In Germany too, we are increasingly seeing Chinese sweet-water cultured pearls being marketed as Japanese, ...

Oldest natural pearl found in Arabia

June 18, 2012

French researchers at the Laboratoire Archéologies et Sciences de l'Antiquité (ArScAn) (CNRS) have unearthed the oldest-ever archeological natural pearl. Discovered at a Neolithic site in the Emirate of Umm al Quwain ...

'Bed of nails' material for clean surfaces

September 17, 2012

(—Scientists at the University of Twente's MESA+ Institute for Nanotechnology have developed a new material that is not only extremely water-repellent but also extremely oil-repellent. It contains minuscule pillars ...

Recommended for you

New method facilitates research on fuel cell catalysts

October 8, 2015

While the cleaning of car exhausts is among the best known applications of catalytic processes, it is only the tip of the iceberg. Practically the entire chemical industry relies on catalytic reactions. Therefore, catalyst ...

Better fluorescent lighting through physics

October 8, 2015

General Electric (GE), Lawrence Livermore National Laboratory (LLNL) and Oak Ridge National Laboratory (ORNL) have created new kinds of fluorescent lighting phosphors that use far less rare-earth elements than current technology.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.