Let's start with a video of tin pest:
From the Wikipedia entry on tin pest:
At 13.2 degrees Celsius (about 56 degrees Fahrenheit) and below, pure tin transforms from the silvery, ductile metallic allotrope of β-form white tin to brittle, nonmetallic, α-form grey tin with a diamond structure. The transformation is slow to initiate due to a high activation energy but the presence of germanium (or crystal structures of similar form and size) or very low temperatures ~-30 degrees Celsius aids the initiation. There is also a large volume increase of about 27% associated with the phase change. Eventually the α-form decomposes into powder, hence the name tin pest.
Tin pest plays a central role in the urban legend that Napoleon's disastrous 1812 invasion of Russia was a disaster because his soldiers' buttons, which were made of tin, turned to grey powder under the harsh, cold temperatures of Russian winter. Yale's Ainissa Ramirez calls it "the world's greatest wardrobe malfunction" in this video. [Update: See also Joe Knight's article in Slate: Napoleon Wasn’t Defeated by the Russians. According to Knight, the real reason is an infectious disease spread by lice.]
The utter calamity of the French invasion of Russia, and the subsequent retreat, is captured so well in Charles Joseph Minard's graphic map, that Edward Tufte calls "the best statistical graphic ever drawn". [see this map for a broader perspective that presents Minard's map with present-day national borders.]
For the Russians, Napoleon's retreat has been a source of intense national pride -- celebrated in major works of art including the 1812 Overture by Tchaikovsky:
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What's the point of all this? Nothing, really; we just happened to be discussing all this in a recent class on the lead-tin phase diagram in my course on materials thermodynamics. Also, I've always wanted to link to Minard's map, the 1812 overture, and the lead-tin phase diagram ;-)