The lamp that came back in the 90s, rebuilt from photos of a Mathmos Astro as it was sold then - the British original from 1963 - down to its hand-spun aluminium base and cap. Tap the base to switch it on: the bulb lights at once, but the wax has to warm up first - about half a minute here, one to three hours in a real one. Then blobs swell out of the glowing pool, rise, cool and sink back, never the same way twice. Tap the cap to put in another bottle - there are five classic colour pairs - and it goes in cold. Never shake a real one: the wax and the liquid turn cloudy, sometimes for good. On a computer, Space or Enter switches it on and off and C changes the bottle. Drag to turn it round.