Research shows that the special mud with which all MLB baseballs are rubbed has unique “magical” properties

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• For years, every major league baseball was rubbed with a special mud before every game to make it less slippery.

• The history of mud dates back to the 1930s, and MLB still relies on one small supplier.

• New research explains why it works: mud has the perfect ratio of clay to sand.

For more than 80 years, baseball has relied on a special mud that takes the shine off the ball’s smooth skin and gives fielders a better grip. The substance is rubbed on every baseball before every major league game.

Called Lena Blackburne Baseball Rubbing Mud, it comes from a single source: a secret location on the banks of a tributary of the Delaware River. Jim Bintliff, a retired printing press operator in New Jersey, collects sludge from his grandfather’s old pit about once a month. He compares its texture after processing to “a cold custard or maybe a stiff pudding.”

Despite the ubiquity of mud, no one has been able to explain the science of why it makes catching balls easier, or even provide empirical evidence that it works at all. Until now.

Researchers from the University of Pennsylvania developed a series of tests to study dirt and even constructed a “finger” made of synthetic rubber to measure its characteristics. Their results, published Monday in the journal Proceedings of the National Academy of Sciencesoffer the first published scientific evidence that the power of mud is more than a myth.

“It spreads like a face cream but sticks like sandpaper. It has this magical ability,” said Doug Gerolmak, a geophysicist at the University of Pennsylvania and co-author of the study.

Jerolmak’s team discovered that the mud had the perfect proportions of sticky clay and sand particles. The latter reinforces the surface of the ball like whisker-shaped shells to increase friction, but the material still spreads thin and uniform, like toothpaste.

“The more you push it, the more it flows,” Jerolmak said.

The authors concluded that any attempt to create a synthetic substance to replace dirt — something that Major League Baseball has been investigating — would be foolish.

“It’s a very special combination of ingredients created by nature that makes it work,” Jerolmak said.

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The history of the origin of dirt goes back to tragedy.

In the game in August 1920. New York Yankees pitcher Carl Mays fired the ball in the direction of the “Cleveland” player Ray Chapman and hit him in the head. Ball struck Chapman in the skull, killing him.

The death raised concerns about wild pitches and the risk of fresh, shiny baseballs slipping out of pitchers’ hands. So in 1929, the president of the National League demanded that umpires start soiling the balls for better grip, according to the Baseball Hall of Fame.

But finding the right substance turned out to be difficult.

“They tried to use the homestead land. It scratched the skin too much. They tried using shoe polish and tobacco spit; those things obscured the ball too much,” Bintliff said.

Finally, in 1938, Lena Blackburn, the third base coach of the Philadelphia Athletics, recalled the finely filtered mud from her childhood in New Jersey. He returned to the source, collected it and began to apply it.

The mud was so popular that Blackburn created a business processing and selling it. He later passed the company on to a childhood friend, with whom he fished and sailed, whose grandson, Bintliff, now runs the company with his wife.

Beginning in 2022, MLB mandated that at least 156 balls be fielded per game, each receiving at least A 30-second mud rub for three hours.

Bintliff said MLB buys mud baths for each team at $100 each — two for the regular season and more for spring training. Some clubs, such as the World Series-winning Dodgers, purchase additional containers for their farm systems, he added.

“This mud works as the finest abrasive and removes the gloss finish without causing any damage to the leather or the laces,” Bintliff said.

He collects dirt in 5-gallon buckets — usually about 10 to 20 buckets per visit to the riverbank — then processes it in his garage by draining the river water, removing branches and rocks, and adding tap water. The process yields approximately 150 pounds of product.

Are there any special ingredients added?

“It’s part of the property,” he said.

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The scientists who studied the mud are not avid baseball players, but they became interested after an informal analysis of the substance five years ago. After that, two students from Jerolmak’s lab set out to see if the mud worked. They developed three key tests.

First, they analyzed the adhesion, or stickiness, of the dirt using an atomic force microscope, which measures the resistance of the dirt when the tool is pulled away from it. Then, to understand how well the slurry flows, the researchers placed it on a machine called a rheometer, which rotated the sample and measured its viscosity.

The third test assessed the friction between human skin and a baseball; it involved the creation of a “finger” made of synthetic rubber, with a drop of whale oil to replace the oils secreted by human skin. The “finger” was pressed against strips of leather baseballs, and then rotated on a rheometer.

According to Emanuela Del Gado, director of Georgetown University’s Institute for Soft Matter Synthesis and Metrology, the properties revealed by these tests are rare and in demand in cosmetics and other fields.

“In industry, people spend quite a lot of time adjusting the formulation to get this type of property,” said Del Gado, who was not involved in the research.

“Simple materials can be extremely complex for us, and they can teach us a lot,” she added, noting that the silt was formed by currents, precipitation and long cycles of seasonal environmental changes.

Today, Bintliff counts college coaches, Little League umpires and National Football League teams among his clients. He plans to transfer the business to one of his children.

So far, mud has outlasted new technologies that are racing to replace it.

In 2016 MLB-tested balls are coated with a proprietary chemicaland last year commissioner Rob Manfred said the league was working with Dow Chemical to create a “sticky ball” that will remain “pure white”. But that draft didn’t end with a solution that could replace dirt, an MLB source said.

The authors of the study recommended against giving up mud, given the new evidence that confirms what ballplayers guessed more than 80 years ago: “This stuff works,” Gerolmak said.