The U. S. Treasury used to have department which would refurbish bills which had gotten dirty (not we hope exclusively dirty money) using a custom-built laundry machine which would soap, scrub, disinfect and iron dollar bills, saving the Treasury from the need to print about $250,000 of new bills each year. Naturally the printers’ unions didn’t like it. Atlas Obscura tells us the story, with a small gallery of photos.
As we learned at the Crane Museum of Papermaking dollar bills (almost exclusively single dollars — we seem to be able to remember to remove larger bills from our pockets — often inadvertently go into the wash. This has the effect of washing off the potato starch with which our currency is coated, an absence which can be detected with a fluoroscope. Of course we all have one of those lying around, don’t we?