Lava lamps are so last century. They were, of course, big in the 80s. I think I’ve actually said somewhere before that I think Lava Lamps were about the pinnacle of human innovation in the 20th century.
Sadly, they could have been invented centuries beforehand had people not been so reliant on electricity. See, all you need is heat, waxy stuff and coloured liquid. And the heat, well, it can come from tea light candles… and now you can buy a lava lamp 1680s style… 
