What determines the cost of synthetic diamonds?
To be honest, I don’t know all the exact details because manufacturers like to keep that to themselves. But, the CVD (chemical vapor deposition) method reduced the amount of energy required to create synthetics. Thus reducing production costs. I imagine that prices will only further drop as technology advances. Ideally, to the point where prices are based on production costs, labor, and supply and demand.
As of November 2018, the synthetic diamond growing industry is working to appeal De Beer’s synthetic diamond pricing with the FTC. According an industry member, it costs them $350 to $400 to grow an eye clean one carat synthetic diamond. You can read more about the drama.
Not all synthetic diamonds are graded the same
When buying quality diamonds, the wholesale industry prefers to find ones with GIA certificates. GIA historically has been the most consistent and reputable lab for grading higher end diamonds. Other labs give similar results, but offer less prestige. Synthetic diamonds come with certificates from a different lab. Personally, I would not buy a sizeable natural diamond if it did not have a GIA grading certificate. And unfortunately, GIA does not grade synthetic diamonds. They will identify the diamond as synthetic, but will provide no other information about the gem. They have their reasons, but I’m guessing this is to maintain their reputation and ensure good terms with the natural diamond industry.
Many synthetic diamonds will come with certs from a variety of labs. Those labs are usually 1-2 grade more forgiving than GIA standards, so a GIA H color, VS2 clarity diamond might be an I color, SI1 clarity at another.