The Kilogram Put On Some Weight

The International Prototype of the Kilogram in three nested bell jars

Did you gain a bit of weight after the holidays? Take heart, you're not the only one - even the kilogram itself has put on weight:

Using a state-of-the-art Theta-probe XPS machine -- the only one of its kind in the world -- the team have shown the original kilogram is likely to be tens of micrograms heavier than it was when the first standard was set in 1875. [...]
The original kilogram -- known as the International Prototype Kilogram or the IPK -- is the standard against which all other measurements of mass are set. Stored in the International Bureau of Weights and Measures in Paris, forty official replicas of the IPK were made in 1884 and distributed around the world in order to standardise mass. The UK holds replica 18 at the National Physical Laboratory (NPL).
But despite efforts to protect the IPK and its duplicates, industrialisation and modern living have taken their toll on the platinum-based weights and contaminants have built up on the surface.

ScienceDaily has more: here.