Via the magnificent Ben Craven: the officially-mandated cleaning regime for international standard platinum-iridium kilogram prototypes (2Mb PDF download). You have to read this in order to appreciate the subtlety of the process, which begins by scrubbing the thing with a finger wrapped in a solvent-soaked chamois. Genius.

(file alongside ‘ISO standard for making tea,’ which was, I think, the story that got Kevin Marks reading The Daily Grind. Gosh, fame. etc. Oh, and while you’re at it, take a look at Ben’s magnificent never-turning gear train. Double genius.)