The science that makes baseball mud ‘magical’

If you looked closely at the baseballs used in the World Series last month, you would notice that they were covered in a mysterious brown substance.

It was not a mistake, and nothing illegal was found on the balls. It was just mud.

For decades, all the balls used in Major League Baseball have been coated with mud harvested from a secret spot along a Delaware River tributary in New Jersey. Only a few people knew of the exact location and until recently, and only a few knew the exact contents of that mud.

Now researchers have dug deep and found what they consider to be 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 published Monday in The Proceedings of the National Academy of Science.

Their research may be well suited for more than just studying baseball. The researchers say that the techniques they used to understand how baseball mud works could be extended to the development of sustainable materials for construction, agriculture and infrastructure.

“This study helps in trying to find materials in nature that can replace hydrocarbon-based materials that we use today,” said Shravan Pradeep, a chemical engineer, postdoctoral researcher at Penn and another author of the study.

Baseball mud is part of the game’s mythology. Since the 1950s, it has been dug up along the Delaware River and applied to brand-new balls by clubhouse attendants. They grab a dab from a container, apply it to the balls with their hands and leave behind a thin brown film.

The mud is applied because new balls from the manufacturer are glossy and slippery, making them difficult for pitchers to grip. But the league allows the material to be rubbed in, unlike other sticky substances that pitchers have tried to use over the years, which are against the rules.

While the source of the mud is a well-guarded secret, the mud is not difficult to obtain. The authors of the new study bought a small jar of Lena Blackburne Baseball Rubbing Mud from the company’s website for less than $30.

Using various instruments, they measured the composition of the mud, its viscosity, levels of friction and adhesion. They say the mud is composed of clay, tiny particulates of quartz and other minerals, a little sand and a very small amount of material from plants and other living things; it is about 43% water by weight. The basic ingredients alone are neither surprising nor remarkable. What makes the mud special are the proportions of the ingredients, which give the mud two characteristics that seem at odds with one another.

The mud spreads on smoothly, but once it dries it has a slightly rough and sticky aspect. The angular particles of sand seem to play an important role, the researchers found. “The sand grains are glued to the surface by the clay,” Jerolmack said, “and now you have this uniform layer with sand particles that are like barnacles studding the surface.”

This duality, the researchers say, means that the mud, or a similar material, could be used as both a lubricant and a friction agent. The mud also gives the balls a more uniform surface by filling in the pores on the leather, and it can effectively double the contact adhesion, or stickiness, between the ball and the pitcher’s hand.

The company that produces the mud is very secretive about the riverbank from which the mud is harvested, as well as the processing procedures. The researchers assume that some filtering occurs — perhaps to reduce the proportion of sand. There may also be a small additive. But they concluded that, as with many geomaterials, years of production and observation had helped the company arrive at its secret recipe.

“They really know what they are doing,” Jerolmack said. “This stuff has been processed to optimize its properties.”

In recent years, Major League Baseball has sought manufactured alternatives to the mud. But the researchers behind the new study say the age-old product that comes from the ground is effective, and sustainable through tidal replenishment. “You don’t need to go synthetic,” said Paulo Arratia, a professor of mechanical engineering and applied mechanics at Penn.

While the study’s authors said that their methods for studying the mud could be applied to similar materials that one day might replace carbon-intensive construction materials, they conceded that there were other motivations for doing the research. “It’s baseball-related,” Pradeep said, “so it’s fun.”

This article originally appeared in The New York Times.

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