Well I can't honestly say how widespread its use was, but the actual emulsion layer was well hardened and thus would remain intact after removal from the base. Between that and the paper was a plain gelatin layer sans hardener, so that it was insoluble in any reasonably warm water. So the emulsion would indeed slide off, or float away, but in a purposeful way.
I think the main m.o. was to then take the loose emulsion and reattach it to a piece of glass, so in the end you basically have a dry-plate without the hassle of using glass-plates in the field and the added boon of having tons of exposures in a light-weight roll.
A pretty exceptional idea!
And as I learned, shooting on paper gives you a speed "boost", since the white paper reflects a lot of light back onto the emulsion.
thanks i never realized that he was just doing emulsion transfers ...
and all those polaroid transfer people thought they were being so inventive !