I remember hearing about some guys trying to make diamonds a while back. They were having some success using washing-machine size machines that focused enormous pressure on a tiny little sample. That was ten years ago or so.
The Diamond Age is also the title of a science fiction novel by Neal Stephenson. One of the premises of that story is that man has learned to make diamonds and it has opened whole new venues of technological progress. Society as a whole still sucks, but what else is new?
I'm not sure how I got started on this, but when I started looking I wasn't finding much, well, except for a bunch of ads for engagement rings. But eventually I found some bits and pieces. Here are some videos give a pretty good overview of what's been going on.
Growing Synthetic Diamonds
synthetic diamond factory
These lab-grown diamonds are identical to natural ones
How To Make A Diamond - Bang Goes the Theory - BBC O
I also remember watching a video where a guy made diamond from pencil lead using a microwave oven, but I can't find it now, so maybe I just imagined it. If so, I've got a really good imagination because I remember it clearly. In any case he turned a ceramic coffee mug upside down and used the depression in the bottom as a crucible. He laid a couple of leads from a mechanical pencil there and added a couple of drops of oil (mineral? vegetable? my memory is fuzzy on this point). He set another coffee mug on top, this one right side up, so the graphite and oil are semi-contained, and then he fired up the microwave and ran it for I don't know how long. I don't recall what method he used to verify that his experiment worked, but if it did, the crystals were very small. Really bugs me that I cannot find this video.
The older HPHT (high pressure, high temperature) method is still in use and has grown considerably:
|A synthetic diamond factory in China|
|HENAN GAINS CO., LTD, located in Zhengzhou China|
China is producing quantities of gemstone quality synthetic diamonds and shipping them to India where they are cut and made into jewelry.
Considerable effort has also been expended in finding ways to determine whether a diamond is synthetic or natural. One way was to laser engrave some kind of a miniature marking on the edge. Another uses spectroscopy. Natural diamonds usually include a bit of nitrogen and synthetic diamonds don't.