Diamonds, whose only source has been natural deposits of volcanic origin, begin to be synthesized in 1955 from graphite subjected to high pressures and temperatures.
Diamonds of gem quality, however, are not made in this way (or if they are, no one is saying).
In 1941, an agreement had been made between the General Electric (GE), Norton and Carborundum companies to further develop diamond synthesis.
They were able to heat carbon to about 3,000 °C (5,430 °F) under a pressure of 3.5 gigapascals (510,000 psi) for a few seconds.
Soon thereafter, the Second World War interrupted the project.
It was resumed in 1951 at the Schenectady Laboratories of GE, and a high-pressure diamond group was formed with Francis P. Bundy and H. M. Strong.
Tracy Hall and others joined the project later.
The Schenectady group improved on the anvils designed by Percy Bridgman, who received a Nobel Prize for his work in 1946.
Bundy and Strong made the first improvements, then more were made by Hall.
The GE team used tungsten carbide anvils within a hydraulic press to squeeze the carbonaceous sample held in a catlinite container, the finished grit being squeezed out of the container into a gasket.
The team recorded diamond synthesis on one occasion, but the experiment could not be reproduced because of uncertain synthesis conditions, and the diamond was later shown to have been a natural diamond used as a seed.
Hall achieved the first commercially successful synthesis of diamond on December 16, 1954, and this is announced on February 15, 1955.
His breakthrough was using a "belt" press, which was capable of producing pressures above 10 GPa (1,500,000 psi) and temperatures above 2,000 °C (3,630 °F).
The press used a pyrophyllite container in which graphite was dissolved within molten nickel, cobalt or iron.
Those metals acted as a "solvent-catalyst", which both dissolved carbon and accelerated its conversion into diamond.
The largest diamond he produced was 0.15 mm (0.0059 in) across; it was too small and visually imperfect for jewelry, but usable in industrial abrasives.
Hall's co-workers are able to replicate his work, and the discovery was published in the major journal Nature.
He is the first person to grow a synthetic diamond with a reproducible, verifiable and well-documented process.
He leaves GE in 1955, and three years later will develop a new apparatus for the synthesis of diamond—a tetrahedral press with four anvils—to avoid violating a U.S. Department of Commerce secrecy order on the GE patent applications.
