Something called "The Black Bottom" emerged in the dance scene some time around 1926 and and was briefly touted in the media as a competitor to the Charleston. Its origins seem to have been among stage and cabaret performers like Ann Pennington and Stella Doyle. It started as a solo stage dance, and then found it's way into the world of social dancing.
I have come to the conclusion that, in practice, the definition of "Black Bottom" was extremely fluid. In fact, I would venture to say there was no single definitive Black Bottom, only a constellation of different, competing moves and styles all calling themselves the "Black Bottom".
Mostly, it appears that it was supposed to focus more on a simpler, side-to-side, swaying two-step motion (said to resemble pulling your feet out of the mud) and lacked the high kicks of the Charleston; but in reality, I don't think dancers were worrying much about whether the thing they were doing was one or the other. They did the moves that seemed to work for them.
In practice, Charleston was really what ever the dancer decided, at that moment it was, and outside the occasional Charleston contest, no one was worrying about whether something was "correct". The same could be said for the Black Bottom. There were distinct "Black Bottom" songs just as there were distinct "Charleston" songs, and each had a distinctive musical riff. The Black Bottom was what ever a Black Bottom tune told you to do and a Charleston was what ever a Charleston tune told you to do.
And indeed I have yet to find THE definitive Black Bottom. There seem to have been a few competitors for that title as evidenced by the frequent use of adjectives like "original", "real" and "true" on recordings, film shorts and sheet music.
What I think Happened
The Black Bottom gained notoriety from stage performances. The name was both funny and a bit naughty, and was bound to appeal to the sensibilities of the Jazz Age. People read about it in the papers, and found recordings and sheet music in the shops, but many did not see the visual examples of the films or live performances - so they made something up and called it "Black Bottom". This happened spontaneously in any number of places in America and Europe, leading to a profusion of "Black Bottoms" that bear no resemblance to one another.
So, if you feel like dancing the Black Bottom, I would suggest looking at the videos below, picking the steps and moves that appeal to you, and just going with it. These dances are not really about precise adherence to a defined form. The wilder and more improvisational you are, the closer you are to the essence of the dance.
Solo Black Bottom
The solo black bottom appears to distinguish itself from the Charleston in that it has a more sensuous swaying motion, while Charleston is full of wild gyrations and kicks. As such, it also appears to have been an almost exclusively feminine dance. I have yet to find an example of a man and a woman dancing it physically separated but together, as you frequent saw with Charleston. It seems to have been almost exclusively a "party piece" for one or more women to do solo for the benefit of the whole room.
The first video is an example of solo Black Bottom such as you would see from a scantily clad cabaret dancer, as demonstrated by a scantily clad cabaret dancer. It is followed by a second video with more, and different, solo Black Bottoms.
Partner Black Bottom - European Only?
The two videos that follow these show partner variations. Both are European. While the Black Bottom was an American invention, I've yet to find any examples of Americans dancing a partner Black Bottom. While I believe such a thing must have occurred, I just haven't found any film evidence of it.
I realize absence of evidence is not evidence of absence, and a song lyric with a woman telling a man "Don't need your black bottom 'round here" suggests an American masculine style existed - but I haven't found it yet. I'm still looking, and if I ever find it, I will be sure to update this page.
The Videos
This one starts out with a partner Charleston, and then provides instruction on the solo Black Bottom. Go figure.
Partner Black Bottom
Here are the two examples I have so far found of a partner Black Bottom. It's interesting that the dancers in the first one are French, and also amusing that, in French, the title means "Here is the true Black Bottom", which again suggests that there are other Black Bottoms out there whose vérité the film maker disputes. This is a great example of blending Fox Trot with jazzy step variations.
And here's a rather sober and sedate (downright sleepy) English take on the Black Bottom which is, again, very unlike all the other "True" Black Bottoms I have found and appears to be, essentially, how you would do a drag if you were doing a two-step.