Author: Jessica Leigh Hester / Source: Atlas Obscura
Nothing was supposed to change, not ever. The little cylinder, made of platinum and iridium, was supposed to stay the same, locked as it was inside a vault, and sealed within nested bell jars.
That isolated life below the International Bureau of Weights and Measures, near Sèvres, France, was meant to keep the cylinder stable forever.That steadiness was crucial, because the thing itself was crucial. Its mass was exactly, precisely one kilogram, not because that what it registered on a scale, but by fiat—it was the kilogram, and the kilogram was it. In 1889, the General Conference on Weights and Measures had anointed it as the supreme kilogram, the International Prototype of the Kilogram, the one against which all others were measured. And that was that, for a while. It slumbered in its vault, and was only trotted out once every few decades, to be compared to more than a dozen copies stashed around the world—for good measure.
The prototype and its cousins were all treated gingerly. Cleaning might involve nothing more than a gentle massage with a piece of chamois leather dampened with ethanol and ether. Two of the duplicates of Le Grand K, as the cylinder is known, are safe and sound under bell jars in a climate-controlled lab at the National Institute of Standards and Technology (NIST) in Maryland. “We don’t even try to touch them with gloved hands,” NIST scientist Zeina Kubarych recently explained to NPR. “You may rub some atoms off or something,” lead NIST scientist Stephan Schlamminger told National Geographic back in 2015.
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