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Baseball Mud

June 24, 2024

The Boys of Summer is a song by the American musician, Don Henley (b. 1947), founding member and drummer of the Eagles.[1] The lyrics, which evoke the nostalgic theme of summer love were written by Henley, and the song was released on October 26, 1984, in the studio album, Building the Perfect Beast. The phrase, boys of summer, is often used as a synonym for baseball players in the major leagues, although the World Series is played long after the autumnal equinox.

A baseball

A baseball. The leather cover of a baseball is created from two pieces of a shape that's similar to certain hygiene products.

According to MathWorld, The baseball cover was invented by Elias Drake in the 1840s, presumably by a trial and error process.[2]

(Wikimedia Commons image by Tage Olsin. Click for larger image.)

A manufactured baseball has a smooth surface with very little friction, and this makes it hard for a baseball pitcher to throw with great accuracy. Friction allows pitchers to throw the ball with a spin, resulting in a curveball. Pitchers in the early days of baseball enhanced the friction by several ad hoc techniques that included rubbing with tobacco juice from the then ubiquitous chewing tobacco, but more often by rubbing with a mixture of spit and pitcher's mound soil. Lena Blackburne (1886-1968), an infielder and coach for a Philadelphia baseball team, decided to search for a standard material in the late 1930s. Blackburne found silt for a rubbing mud on the New Jersey side of the Delaware River (said to be "near" Palmyra, New Jersey).

The Delaware River is presently notable as costing $3.50 for crossing at the Delaware Water Gap, which is something I do several times during the year, but many times in the past (at $1.00) when my daughter was a college student in Pennsylvania. Blackburne founded a company to sell Lena Blackburne Baseball Rubbing Mud. The American League used the mud soon after its discovery, and it was in use by every Major League Baseball team by the 1950s.

It's nice to make money from something that's dug from the ground with very little processing, and making a considerable profit at this belies the expression, dirt cheap. About a thousand pounds of the silt is harvested each year, and the mud mixture is sieved before it's packaged for sale. Another example of a material that's dug and used with very little processing is kieselguhr, also known as diatomaceous earth, the fossil shells of diatoms. Diatomaceous earth is about as close to a free lunch as a materials scientist can get.

An SEM micrograph of a diatom fossil (CSIRO)

A Scanning electron micrograph of a diatom fossil, looking much like the front end of a microphone I once had.

Some people who are not familiar with diatom fossils have believed that what they have discovered are pieces of some extraterrestrial artifact.

Diatom fossils are just a few tens of micrometers in size.

(CSIRO image. Click for larger image.)

Diatomaceous earth is a mixture of silica (SiO2, 80-90%), alumina (Al2O3, 2-4%) and iron oxide (Fe3O4, 0.5-2%). This mixture of inorganic oxides can be used to thermally insulate high temperature furnaces. Diatomaceous earth is also used as an abrasive, a filtration medium, a support medium for catalysts, and a filler for plastics. The absorbency of diatomaceous earth makes it useful for cat litter, and also as a way to stabilize nitroglycerin to form dynamite.

Baseball mud has the surprising property that it spreads like an expensive face cream, but it contains a considerable quantity of sand.[3] A scientific study of the material properties of baseball mud has been undertaken by a group of geophysicists and mechanical engineers from the University of Pennsylvania (UPenn, Philadelphia, Pennsylvania).[3-4] The team is led by Douglas Jerolmack, a professor of Earth and Environmental Science at UPenn, and it includes postdoctoral research associate, Shravan Pradeep, and mechanical engineering student, Xiangyu Chen.[4]

Jerolmack's interest in baseball mud started in 2019, when a sports journalist asked him to analyze a sample of the mud.[3] Jerolmack's cursory analysis of the material showed its composition to be a mixture of sand, silt, clay, and water, and there was no clue to its special properties.[3] Further viscosity testing revealed a property called shear-thinning for which a material thins with applied force, and this allows creation of a very thin layer of mud on the baseball.[3]

As the research continues, its suspected that trace components of the mud beyond sand, silt, clay, and water, might be responsible for it's special properties.[3-4] Two such components may be organic chemicals from decaying plant matter and microbial secretions.[3] Jerolmack thinks that with enough research, he could make a version of his own, not to compete with baseball mud, but for use as an industrial lubricant.[3] Major League Baseball has searched for an alternative material to the mud, and it's tested balls treated chemical additive from Dow Chemical.[3] The motivation, of course, is quality control year over year, and resistance to having just one supplier of the material.


  1. Don Henley, "The Boys Of Summer," official music video, via YouTube.
  2. Eric W. Weisstein, "Baseball Cover," MathWorld (A Wolfram Web Resource).
  3. Tom Avril, "What's so ‘magic' about the secret South Jersey mud rubbed on baseballs? These Penn researchers think they know why," The Inquirer, October 27, 2023.
  4. Nathi Magubane, "The alchemy behind the diamond: Unearthing baseball’s beloved mud," University of Pennsylvania Press Release, October 30, 2023.

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