Marbling, whether of the infant playgroup or of the fine bookbinding variety uses the technique of flotation-printing, i.e. of floating colours onto a prepared solution of a water-based thickener . If you are interested in trying this art/craft check the internet for materials & techniques (there are many and various ways of producing interesting work on both paper and fabric).
The examples presented here derive from floating dilute oil-colours onto a thin cellulose gum – the resulting patterns (whether simply cumulative or stirred can be lifted by carefully laying a piece of paper on the surface.
My own experience of this technique goes back to the 1960s when I was involved in a workshop, Koraz, that produced wall-sized marblings for interiors. Since that time it has been an occasional diversion (rather than the obsession that it can become. Beware).
 The tradition method for this uses Carragen Moss, but commercial methylcellulose gums offer a cheaper alternative these days.