Grown In A Reactor: The Arithmetic Of The Synthetic Diamond

AA diamond is nothing more than carbon arranged in one particular lattice, and nothing in that lattice requires a volcano to produce it. Two industrial routes now exist. The older, high-pressure high-temperature synthesis, has turned out abrasive grit since the 1950s and still does. The younger, chemical vapour deposition, builds a crystal layer by layer out of a heated gas and became capable of gem quality only in the past two decades. Until about 2015 the output of both was too small and too discoloured to trouble a jeweller; by 2023 stones grown in reactors accounted for roughly one engagement ring in six sold in the United States. The argument that followed has rarely been about whether such objects are diamonds, a question the laboratories settled long ago, but about which of the claims printed beside them in shop windows can actually be defended. Almost all of those claims concern the environment, and almost all were written by people who had measured nothing.

BFabio Rautio, a materials scientist at the Delft Institute of Crystal Growth, argues that whatever advantage the grown stone enjoys belongs to the electricity supply rather than to the technique. Between 2016 and 2022 her group collected metered consumption from twelve commercial reactors on three continents and recorded the power drawn for every finished carat. The median came to 218 kilowatt-hours, but individual plants ranged from 96 to 740, a spread wider than the whole difference usually quoted between grown and mined stones. Efficiency did improve across the period: the median fell by about two fifths as reactors were enlarged and run in longer cycles. What did not fall was the number of plants sitting on grids where coal supplied most of the generation, which stood at eight of the twelve when the survey opened and eight when it closed. An average for the industry, Rautio maintains, therefore describes no actual factory.

CThe claim yields a prediction, and Rautio has tested it. If the saving belongs to the grid, then stones grown where the current is dirty should compare badly with mined ones however modern the vessel that made them. In the eastern province holding four of her plants, where coal supplied 78 per cent of generation in 2021, the carbon attributable to a one-carat stone came to 141 kilograms, against about 108 kilograms for the mined benchmark her group had adopted. The reduction advertised by retailers appeared only at plants standing on grids that drew more than half of their power from nuclear or hydroelectric generation. The asymmetry matters commercially, since the regions that grow the most stones are also the regions with the cheapest coal. Rautio is nonetheless careful to present the result as a limit on one advertising claim rather than a judgement on the technology.

DKalinda Nilsen, a resource economist at the Kimberley School of Mineral Economics, rejects the comparison itself, on the ground that the mined figure is drawn too narrowly. Published emissions for a mine, he points out, usually stop at the pit gate, leaving out the rebuilding of waste rock and the treatment of water that continues for decades after closure. His 2020 audit of seven open-pit operations found that counting those obligations raised the figure for each carat by 34 per cent. Boundaries of this kind are argued about openly in the sector now, although they were rarely questioned when he began. A comparison in which one side is measured to the pit gate and the other from the wall socket, Nilsen says, reports the habits of accountants rather than anything about diamonds. He concedes two things, however. All seven mines lay within a single country, and the rehabilitation costs were taken from company disclosures because no independent audit of them exists.

EThe dispute long ago left the journals. When the advertising regulator of one large market struck the word natural from its definition of a diamond in 2018, retailers acquired a licence to sell grown stones without qualification, and the wholesale price of a one-carat grown stone fell from about 4,200 dollars that year to under 900 by 2023. Nilsen observes that several southern African economies raise a fifth of their export earnings from mining, so that a collapse in price is a question about work before it is a question about carbon. Rautio, uncomfortably for her own position, points out that nothing in her energy accounts bears on whether the trade is fair, since carbon and livelihoods are not alternatives. Both regret that the loudest figures in the debate are published by the firms with most to gain from them.

FA settlement of sorts is taking shape in which the two accounts are assigned to different questions rather than ranked against each other. Where the question is how much carbon a particular stone carries, the answer depends on the meter attached to one particular building, which is why national averages have proved so useless. Where the question is what the change costs the people who dig, no meter helps and the arithmetic has to be done in wages. The unresolved point is whether cheap grown stones will displace mined sales or simply enlarge the market for jewellery as a whole, and no dataset now available can separate those outcomes. What both researchers reject is the assumption that the origin of a stone settles anything by itself.