Praseodymium was isolated in 1885 by the Austrian chemist Carl Auer von Welsbach, who split a substance long thought to be a single element, didymium, into two. He named one half praseodymium, from the Greek prasios didymos, green twin, after the green colour of its salts. It is a soft, silvery rare-earth metal used in strong magnets, in the yellow-green glass of welders' goggles, and in high-strength alloys. It is used with neodymium in strong permanent magnets and in the didymium glass that shields the eyes of welders and glassblowers from glare, and it lends a clear yellow colour to ceramics and glass.
Auer von Welsbach was one of the most commercially successful chemists of his era: besides splitting didymium, he invented the incandescent gas mantle that bears his name, still recognisable in camping lanterns today, developed the flint alloy used in modern cigarette lighters, and pioneered an early metal-filament electric lamp, so the same rare-earth chemistry that yielded praseodymium and neodymium also quietly lit homes and streets across turn-of-the-century Europe. His Vienna-area factory at Treibach became one of the first industrial centres for rare-earth extraction anywhere in the world, processing the same monazite sands that would later also yield thorium.