"The process works by placing a tiny fragment of diamond (called a carbon seed) into a microwave along with varying amounts of a carbon-heavy gas - methane is most commonly used. The gas mixture is heated to very high temperatures in the microwave to produce a plasma ball, and inside this, the gas breaks down and the carbon atoms crystallise and accumulate on the diamond seed, causing it to grow.
"The process can take up to 10 weeks to produce a marketable diamond, but it works so well, experts reportedly need a machine to tell the lab-grown gems apart from natural ones sourced from mines or riverbeds." http://www.sciencealert.com/here-s-how-you-can-make-perfect-diamonds-in-the-microwave
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