Aqua regia, literally meaning “King’s water”, is a highly corrosive mixture of acids; it is the only mixture of acids that can dissolve gold.
Hungarian chemist George de Hevesy dissolved the nobel prizes of his peers in aqua regia during the German invasion of Denmark in WWII to prevent Nazis from looting the prizes. He placed the liquid solution of gold and aqua regia in plain sight where it was overlooked. After the war had ended, de Hevesy returned to precipitate the gold out of the mixture. He then returned the gold back to the Nobel Foundation where it was then cast back into its original shape. (img)
“The Quarter Shrinker uses a process called High-Velocity Metal Forming to create extremely powerful pulsed magnetic fields. We use these fields to squeeze a coin, forcing it to rapidly shrink in diameter. There is no direct contact with the coin – all of the reshaping is done by invisible and incredibly strong magnetic fields! The Quarter Shrinker forces a huge current pulse (up to 100,000 amperes!) into a 10-turn work coil made from insulated copper wire. A coin is previously centered within the work coil. Through transformer action, a current of up to one million amperes is induced within the coin. The instantaneous power applied to the coil is comparable to the total electrical power consumed by a medium-sized city. Another phenomenon, called “skin effect”, forces this immense current to flow within a circular ring that’s only 1/20” thick along the edge of the coin. The immense circulating current within the rim of the coin creates another powerful magnetic field around the coin. The magnetic fields from the work coil and the coin oppose each other - an effect called “Lenz’s Law”. This results in tremendous magnetic repulsion forces between the work coil and the coin. Compressive forces squeeze the coin inward, reducing its diameter while simultaneously making it thicker. The entire process is over in less than the blink of an eye (~25 millionths of a second!). The coin becomes extremely hot from the combination of rapid mechanical deformation and resistive heating.” Via.