If you are interested, a good book on that subject is "Complicity." This is from the front dust jacket flap:
"Slavery in the South has been documented in volumes ranging from exhaustive histories to bestselling, novels. But the Norths profit from—indeed, dependence on—slavery has mostly been a shameful and well-kept secret... until now. In this startling and superbly researched new book, three veteran New England journalists demythologize the region of America known for tolerance and liberation, revealing a place where thousands of people were held in bondage and slavery was both an economic dynamo and a necessary way of life."
"Complicity reveals the cruel truth about the Triangle Trade of molasses, rum, and slaves that lucratively linked the North to the West Indies and Africa; discloses the reality of Northern empires built on profits from rum, cotton, and ivory—and run, in some cases, by abolitionists; and exposes the thousand-acre plantations that existed in towns such as Salem, Connecticut. Here, too, are eye-opening accounts of the individuals who profited directly from slavery far from the Mason-Dixon line—including Nathaniel Gordon of Maine, the only slave trader ever sentenced to die in the United States, who even as an inmate of New York's infamous Tombs prison was supported by a shockingly large percentage of the city; Patty Cannon, whose brutal gang kidnapped free blacks from Northern states and sold them into slavery; and the Philadelphia doctor Samuel Morton, eminent in the nineteenth-century field of "race science," which purported to prove the inferiority of African-born black people."
[Farrow et al, "Complicity: How the North Promoted, Prolonged, and Profited from Slavery." Ballentine Books, 2005, Front Jacket Flap]
Chapter 10, titled "Plunder for Pianos," exposes hypocritical abolitionists who opposed slavery, on the one hand, but supported it when it came to obtaining supplies for their ivory business.
Mr. Kalamata
Thanks, will try to get a copy.