First and foremost, lab-grown diamonds (real diamond, but not mined) are in fact available for jewelry purchase, but on a limited basis. The significant catch though is this – when most people think of a diamond, they automatically think of white diamonds. As of October, 2007, no one is currently able to offer white (colorless) lab grown diamonds for sale on any type of production basis. Regardless of what various reporters write, the reality is only fancy color diamonds (predominantly yellow, and to a much lesser degree, pink and blue) are available.
The reason for that gap between what consumers want (white lab-grown diamonds) and what labs can deliver (mostly yellow lab-grown diamonds), is due to both commercial value and natural barriers. Lets discuss the natural barrier first – yellow diamonds are yellow because they incorporate nitrogen into their crystal structure. White diamonds are white (or clear) because they have much less nitrogen in their crystal structure. When growing diamonds, however, nitrogen is a catalyst – it significantly speeds up diamond diamond growth, and in addition reduces defects. Thus, you can grow a 1ct (finished) yellow in roughly one week, versus growing the same size white (by restricting nitrogen) can take you 4-6 weeks (using BARS method, the default method currently). In other words, nitrogen can help you grow up to 6x as much yellow diamond as white in the same amount of production time. That’s a tough natural barrier.
The commercial barrier, is that yellow natural diamonds are worth much more than white natural diamonds. In nature, there are roughly 10,000 whites for every fancy yellow. Thus, fancy yellows command a much higher price per carat. Lab grown diamonds typically sell at a discount but are still pegged to their natural counterparts, and since yellow diamonds are worth more than whites, the absolute selling price for lab grown yellows is higher than what the market will pay for lab grown whites.
Now, if you combine the fact that labs can grow yellows much more quickly and easily than whites, and that yellow diamonds (lab grown and natural) further command higher prices than whites, you can see you have a severe dis-incentive to produce white diamonds with the current technology. White diamonds can and have been produced by labs (we have some sample photos on our website) but they are not price competitive with natural white diamonds at this time. Hence, a very big reason for why there are currently no white diamonds available for commercial sale.