What was Thomas Paine's stance on slavery?

Paine was a staunch abolitionist despite the fact that he never wrote on the subject. The biographies on Paine are in error when they attribute "African Slavery in America" and "A Serious Thought" to Paine, and Paine was not a founding member of the first abolitionist organization established in Philadelphia in 1775. However Paine always called for the abolition of slavery in personal corresondence and was close friends with many of the leading abolitionists of his day. See, for example, To Benjamin Rush March 16, 1789. Also see Mariam Touba's essay.