For decades, all the baseballs used in MLB games have been covered with mud harvested from a secret location along a Delaware River tributary in New Jersey, writes David Waldstein for The New York Times.

After several years, researchers are now digging deep to discover the exact contents of that mud.

So far, they have found some remarkable mechanical properties of this mud.

“This is the magical thing: It spreads like face cream and grips like sandpaper,” said Douglas Jerolmack, a professor of earth and environmental science at the University of Pennsylvania and one of the authors of a paper in The Proceedings of the National Academy of Science.

Baseball mud has been dug up along the Delaware River and applied to brand-new baseballs since the 1950s. Clubhouse attendants grab a dab from a container, apply it to the balls, and leave behind a thin brown film.

They apply the mud because new balls are often glossy and slippery, which make them difficult for pitchers to grip.

The mud is composed of clay, tiny particles of quarts and other materials, a bit of sand, and a very small amount of material from plants and other living things.

Read more about the magic behind the mud rubbed on baseballs in The New York Times.

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