Is this the one the freed slaves actually paid for?
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Yes, I believe it was, along with a dedication ceremony speech by Frederick Douglass.
The statue in Boston is a copy of the Emancipation Memorial in Washington DC. The latter is the one that the freedmen actually paid for. The Boston statue was a gift of a civic minded benefactor, who thought that emancipation, freedmen, and the martyred Great Emancipator were worthy of commemoration and remembrance. Clearly he was not progressive enough for Boston today.
I do not know if the Boston copy was made from the original mould by the original artist.