Ever turn off your lava lamp but after it cools down it's stuck in a funny shape?

@ArishMell Your impression is correct; they did go out of fashion for a while. The original manufacturer, Crestworth Trading in Poole, Dorset (now Mathmos) scaled back production to a trickle. Over the last few decades they've revived and become a kind of cultural constant and in spite of the knock-offs Mathmos has survived.