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A dried-up mold sample just sold for $15,000

A hefty auction price for a strange mold sample makes sense once you know its origin story and all the extras that came with it.

That's some expensive old mold.

How much would you pay for some really old mold? How does $15,000 sound? London auction house Bonhams dropped the gavel on a £12,500 sale for a cracked glass disc with a sample of dried-up penicillin mold on Wednesday.

The mold traces back to Scottish biologist and Nobel Prize winner Alexander Fleming, known for discovering in 1928 that penicillin could be used as an antibiotic substance. This helped kick off the modern era of antibiotics.

To be fair, the auction price included a lot more than just a dried-up patch of mold. The lot also contained Fleming's loose-leaf notes from a visit to France, a draft of an address given at the birthplace of Louis Pasteur, a collection of signed letters, a notebook Fleming kept during a US visit, an engraved visiting card and quite a bit more ephemera.

The auction lot, which also includes family snapshots, originated with Fleming's niece Mary Elizabeth (Anne) Johnston, giving it excellent provenance. The mold sample is inscribed on the back with "The Mould which makes Penicillin/Alexander Fleming."

This isn't the first time one of Fleming's mold samples has commanded a high price at auction. Bonhams sold another dried-up bit of penicillin mold in late 2016 for over $46,000 (£37,500, AU$61,000). That auction lot also included some letters.

Bonhams did not reveal the identity of the buyer, but the mystery person now owns a small treasure trove of Fleming-related documents and memorabilia, which makes that $15,000 price tag sound a lot more reasonable.

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