Praseodymium

Praseodymium and neodymium were separated out of a substance called didymium in 1885 by Carl Auer von Welsbach, who found that what Mosander had taken for a single element was two; the names mean green twin and new twin. Praseodymium glass filters the sodium-yellow glare out of a glassblower's or welder's field of view without dimming everything else, which is why the goggles look green. Commercially it is rarely separated from neodymium at all — the mixed "didymium" metal is fed straight into NdFeB magnet production, where praseodymium substitutes for neodymium at a few percent and costs less.