What is an "Artificial Nigger"

Reading this story, I find myself confused as to what the titular "Artificial Nigger" is and why. The statue is obviously connected with the concepts of mercy and redemption for Mr. Head, but how? This is still unclear to me. Throughout the story (before the introduction of the statue) I wondered if Mr. Head and Nelson are, in some way, "Artificial Niggers" within this city. In this urban setting, the two rural characters find themselves confused, without shelter, food or money, and ostracized. Is this analogous to the treatment of African-Americans in post-Emancipation America? At one point the narrator notes that Nelson and Mr. Head look into the rich (white) stores but do not go in, perhaps drawing a connection between rural/urban divide and racial segregation. Earlier, Mr. Head remembers being mocked out of a (presumably white) department store, perhaps another example of the undeserved ostracism that characterizes the main character's interactions with the city. Although these characters are vehemently, unrepentantly racist, perhaps they fail to realize that in the city, they too are "niggers" - that which is deemed base, deplorable, and insignificant by the dominant social structure. At other points it seems that Nelson may also be an analogue for "nigger," when he is in trouble on the street and Mr. Head denies them. I think this could refer to the failure of reconstruction to support freed-slaves and help them integrate into society as equals; the American government essentially denied their existence as rightful "sons" of this nation much as Mr. Head denies Nelson when he is needed most.
As for how all this rambling ties in with the statue and redemption, I'm at a loss. Any comments or help would be appreciated.