Liquid light shows surfaced on both sides of the Atlantic around 1966 and were an integral part of the psychedelic music scene well into the seventies.
Shows could be as simple as a single operator and two or three modified slideprojectors or overhead projectors and a couple of color wheels or as complex as shows with ten or more operators, 70 plus projectors (including liquid slide, liquid overhead, movie and still image models plus a vast array of highly advanced (for the time) special effects equipment).
Second, American shows were generally built around the overhead projector with the liquids in large clock cover glasses.
The surface tension of the liquids largely retained the mixtures between the glass slides, but the process was nevertheless very messy indeed and operators had their hands almost permanently stained by the dyes.
A popular choice of colored liquids for light shows was Flo-Master ink, a product developed for use in permanent marker pens, also Vitrina which was intended for painting on glass.