Sorry, hit the send button too soon.

I also intended to mention that folk music historians aren't very knowledgeable about this music. One is better off going to dance history and theatre history sources. The black face minstrel phenomenon did grow out of the English music hall tradition, just as vaudeville grew out of minstrel shows.

As to the black face tradition among English/Welsh mummers/morris dancers, though I haven't studied it, I believe it could well have come into being after the American minstrel shows toured Britain. If you look at the photographic and memorabilia evidence, the way they are made up in both countries is virtually identical.