I will have to try the tobacco and the soda ash. If Min doesn't respond to this thread I will PM.
I did try letting the sheen go off of the base slip before I put the stained vinegar on it. Absolutely nothing happens when I do that. I don't even have a little fragment dendrites around the edge of my blobs. In the Robin Hopper Video, it looks like the base slip is very wet.
I think you are right now that I think of it. i think the slip has to be wet. you put some kind of stain in the tobacco juice like iron ox., and it forms these tree like structures. Saw it done about 20 years ago, so i may not have it right, but I am very sure that it was tobacco that they used. they were pretty cagey about it at the pottery I visited in the states, calling it a rare herb. i laughed, because I knew tobacco when I saw it.