Lena Blackburne spent six of his 8 completely unremarkable MLB seasons with the White Sox. However, in the 1930's, after his retirement, Blackburne made a remarkable discovery that became crucial for baseball. Today, Blackburne's family continues marketing his discovery to baseball teams at many levels. Identify this product the source of which remains a Blackburne family/corporate secret, but which many suspect comes from the banks of the Delaware River.
Baseball rubbing mud