As HPHT method involves using metal catalyst, it is hard to avoid some metals entering the crystal during growing process, so HPHT diamonds might be magnetic. And if the magnetism is too strong, diamonds will not be able to pass the diamond teste. Because CVD diamonds are formed by mere gas, they can be produced without magnetic and are able to pass the diamond tester pen.
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As society developed and people's living standards rose, they slowly reached a point where they could accept artificial diamonds. As a result, jewelers began to make diamond rings with synthetic diamonds.
However, it was not until 1970 that gem-quality diamonds with large grains were synthesized by the American company General Electric. After nearly thirty years of effort, it is now possible to obtain crystals as large as a dozen carats, but the cost of gem-quality diamond synthesis is still too high to allow for mass production. only 3,500ct of synthetic diamonds could be cut and ground in 2000, representing only 0.01% of natural gem-quality diamond production that year.
As a result of the technological advancement of man-made diamonds, the quality of man-made diamonds is now very high. From the naked eye alone, we can no longer tell whether a diamond is lab grown diamond or not.