The first diamond anvil cell at the NIST Museum, from The Diamond Anvil Pressure Cell [pdf] by Gasper J. Piermarini and Stanley Block
The Diamond Anvil is a simple lab device that scientists use to create pressures as great as those found at the center of the Earth. It's called that because it actually uses diamonds - one of the hardest substances known to man - to squeeze things at pressures as high as 300 gigapascals or 43,500,000 psi.
The principle behind the diamond anvil is quite simple: put something between the flat surfaces of two brilliant-cut diamonds in a contraption like the one shown in the left below, and then turn the screws to push the diamonds together. Whatever is placed between the diamonds is then pressurized. But don't get excited about the diamond: they're just about a third of a carat big.
The very first Diamond Anvil Cell was handmade by Charles E. Weir in the late 1950s at the National Bureau of Standards. He used regular shop equipments like a lathe, drill press, hack saw, soldering gun, threading tools, files, and a high speed grinding wheel to polish down the diamonds to form the anvil faces. He got the diamond for free, from smuggled contraband diamonds confiscated by the government.
Source: The Diamond Anvil Pressure Cell [pdf] by Gasper Piermarini and Stanley Block.