This is pretty cool. First off, I didn't know that the NYC Municipal Archives/NYC Department of Records and Information Services had a website with digital galleries and images of current exhibitions (I unfortunately missed that Robert Moses exhibition).
One of the online galleries they have currently on display (that's a weird thing to say about a website) is this collection of records of slavery and emancipation papers.
Slavery was introduced into New Amsterdam by the Dutch West India Company (DWIC) in 1626. The first slaves were 11 men whose labor was owned by the DWIC and not by individual residents of the colony. The company desperately needed laborers to erect buildings, construct roads and grow food. Slavery continued uninterrupted until 1827.
In 1799 the New York State Legislature passed an “Act for the Gradual Abolition of Slavery” which granted freedom to all children born of slave women after July 4, 1799. However, the children were required to serve a period of indenture to the slave owner; males until the age of 28; females until the age of 25. After this period of servitude they would become free.