Part of not finding it earlier is because you're looking in the wrong place: Grimaldi blacked up, as did the guy playing Othello, the Moor of Venice. Will Kemp, from the same company, was renowned as a morrisman, and may have had a hand in the build of the play (1601-3), although he was dead by the time it was staged in late 1603. We know that the early morris came from these same Court circles at the same time, making the proximity of theme more than tempting.

It's only once morris leaves the stage in the Restoration that you'll find blackface as a tradition. By that time the slave trade was well established, and so it's also part of a social discrimination: what might originally have been a mostly ignorant attempt at cultural integration had by then become somewhat derogatory. And so it remained.

The question of blackface comes from an entirely different and utterly racist origin, the minstrel tradition of the US. Extending it into the folk domain is probably excessive, as there is no common ground: the folk world is not derogating or being in any way abusive of people of African descent. IF there were tunes which did so, then there would be a case. However, the race card is being overplayed of late to the extent where it is actually being used in reverse racism, as a way of making it impossible to criticise people of that ethnicity (Manchester child abuse police problems being a case in point). In practice, it is simply racism in reverse, colour on white, and that we should no more tolerate than white on anyone else. We're people, folks, and skin colour should make fuck all difference either way.

The answer, then, is not to black up black on black, but as camo, and collect for one of the veterans charities. That makes this untouchable!