(Reuters) - The growing acceptance of man-made diamonds by millennials has spurred De Beers to reverse its policy of shunning the sector for jewelry and to launch its own laboratory-grown diamonds through its Lightbox jewelry brand.

The move potentially threatens the profits of rival lab-grown gem producers but could also undermine De Beers’ natural diamond business if it broadens the appeal of stones created in a lab.

Below are details of man-made diamonds:

ORIGINS

A team at the General Electric Research Laboratory in New York discovered the first commercially successful process for producing man-made diamonds in December, 1954, according to the book “The Diamond Makers” by Robert Hazen.

Scientists had been seeking to create a diamond since the discovery in 1797 that diamonds, the hardest natural substance on earth, were made of nearly pure carbon.

PROCESSES

There are two main methods to produce man-made diamonds:

HPHT

The High Pressure, High Temperature process, which was used by the General Electric scientists in the 1950s, seeks to replicate the way natural diamonds were formed about 100 miles beneath the earth millions of years ago.

It uses pressure of more than 1.5 million pounds per square inch and temperatures above 2,000 degrees Celsius in a machine to transform carbon into diamonds.

Scientists at Element Six, part of Anglo American, AAL.L liken the pressure required to standing the Eiffel Tower upside down on a drinks can.

By the 1990s the technique became advanced enough to create diamonds of sufficient quality and size to be commercially viable.

CVD

The Chemical Vapour Deposition process, which became viable in the 1980s, does not require high pressure.

A hydrocarbon gas mixture is ionized by microwaves or lasers in a vessel at temperatures of about 800 degrees Celsius. This breaks the molecular bonds of the gases, spurring carbon atoms to be deposited on a diamond seed, growing into a crystal, layer by layer over days and weeks.

Many of the new lab-grown diamonds companies use CVD, which gives the diamond creator greater control over the process, making it suited to production of large volumes of gem-quality diamonds rather than industrial-quality stones for purposes such as cutting machinery.

MARKET

The lab-grown diamond jewelry market was worth $1.9 billion this year and is forecast to grow 22 percent annually to $5.2 billion by 2023 and $14.9 billion by 2035, analyst Paul Zimnisky said.

The man-made sector is worth about 2 percent of the total $87 billion diamond jewelry market and is due to increase its share to 5 percent by 2035, according to Zimnisky.

MILLENNIALS

A poll of 2,000 female millennials by Berenberg Research found that 53 percent would happily accept a lab-grown diamond engagement ring - with acceptance ranging from 62 percent in Japan to 56 percent in the United States and 40 percent in China.

PRICES

A 1 carat round-cut natural diamond with high gradings of clarity (VS1) and color (D) is listed for $5,970 on the Brilliant Earth here website while a lab-grown diamond with the same gradings is listed at $3,775, a discount of 37 percent.

This year alone, the average discount of lab-grown diamonds to natural diamonds widened to 42 percent by mid-November from 29 percent in January, analyst Zimnisky said.

De Beers' lab-grown jewelry company Lightbox lightboxjewelry.com is selling 1 carat diamonds for $800 without grading reports, a discount of 80 percent or more to natural diamonds, depending on the grading. Lightbox, however, neither sells loose diamonds nor engagement rings, only fashion jewelry such as necklaces.

De Beers is owned by mining company Anglo American AAL.L.

The retail price of a gem-quality man-made diamond has nearly halved over the past two years while wholesale prices have dropped threefold, consultants Bain & Company said in a report this month.

COSTS

The cost of creating a lab-grown diamond has dropped to $300-$500 per carat using the CVD method, compared with $4,000 per carat in 2008, the Bain report said.