The Verneuil method (or Verneuil process or Verneuil technique), also called flame fusion, was the first commercially successful method of manufacturing synthetic
gemstone
A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, when cut or polished, is used to make jewellery, jewelry or other adornments. Certain Rock (geology), rocks (such ...
s, developed in the late 1883
by the
French chemist
Auguste Verneuil. It is primarily used to produce the
ruby
Ruby is a pinkish-red-to-blood-red-colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sapph ...
,
sapphire
Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, cobalt, lead, chromium, vanadium, magnesium, boron, and silicon. The name ''sapphire ...
and
padparadscha varieties of
corundum
Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium, and chromium. It is a rock (geology), rock-forming mineral. It is a naturally transparency and translucency, transparent material, but ...
, as well as the
diamond simulant
A diamond simulant, diamond imitation or imitation diamond is an object or material with gemology, gemological characteristics similar to those of a diamond. Simulants are distinct from synthetic diamonds, which are actual diamonds exhibiting t ...
s
rutile
Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite.
Rutile has one of the highest refractive indices at vis ...
,
strontium titanate and spinel. The principle of the process involves melting a finely powdered substance using an
oxyhydrogen flame, and crystallising the melted droplets into a
boule. The process is considered to be the founding step of modern industrial
crystal growth
Crystal growth is a major stage of a crystallization, crystallization process, and consists of the addition of new atoms, ions, or polymer strings into the characteristic arrangement of the crystalline lattice. The growth typically follows an ini ...
technology, and remains in wide use to this day.
History
Since the study of
alchemy
Alchemy (from the Arabic word , ) is an ancient branch of natural philosophy, a philosophical and protoscientific tradition that was historically practised in China, India, the Muslim world, and Europe. In its Western form, alchemy is first ...
began, there have been attempts to synthetically produce precious stones, and
ruby
Ruby is a pinkish-red-to-blood-red-colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sapph ...
, being one of the prized
cardinal gems, has long been a prime candidate. In the 19th century, significant advances were achieved, with the first ruby formed by melting two smaller rubies together in 1817, and the first microscopic crystals created from alumina (
aluminium oxide
Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula . It is the most commonly occurring of several Aluminium oxide (compounds), aluminium oxides, and specifically identified as alum ...
) in a laboratory in 1837.
By 1877, chemist
Edmond Frémy had devised an effective method for commercial ruby manufacture by using molten baths of alumina, yielding the first gemstone-quality synthetic stones. The
Paris
Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, largest city of France. With an estimated population of 2,048,472 residents in January 2025 in an area of more than , Paris is the List of ci ...
ian chemist Auguste Verneuil, who applied to work with Frémy at age 17, became
Frémy's assistant in 1876 and helped develop the method,
but soon went on to independently develop the flame fusion process, which would eventually come to bear his name.
One of Verneuil's sources of inspiration for developing his own method was the appearance of synthetic rubies sold by an unknown
Geneva
Geneva ( , ; ) ; ; . is the List of cities in Switzerland, second-most populous city in Switzerland and the most populous in French-speaking Romandy. Situated in the southwest of the country, where the Rhône exits Lake Geneva, it is the ca ...
n merchant in 1885.
These "Geneva rubies" were determined to be artificial at the time but are now believed to be the first rubies produced by flame fusion, predating Verneuil's work by several years. After being introduced to the "Geneva rubies" by a mineralogist at the Natural Museum of History in Paris, Verneuil came to the conclusion that it was possible to recrystallise finely ground aluminium oxide into a large gemstone. This realisation, along with the availability of the recently developed oxyhydrogen torch and growing demand for synthetic rubies, led him to design the Verneuil furnace, where finely ground purified alumina and
chromium oxide were melted by a flame of at least , and recrystallised on a support below the flame, creating a large crystal. Verneuil documented his work in sealed documents during the 1890s and publicly announced his work in 1902, publishing details outlining the process in 1904.
By 1910, Verneuil's laboratory had expanded into a 30-furnace production facility, with annual gemstone production by the Verneuil process having reached in 1907. By 1912, production reached , and would go on to reach in 1980 and in 2000, led by
Hrand Djevahirdjian's factory in
Monthey,
Switzerland
Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...
, founded in 1914. The most notable improvements in the process were made in 1932, by
S. K. Popov, who helped establish the capability for producing high-quality sapphires in the
Soviet Union
The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
through the next 20 years. A large production capability was also established in the
United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
during
World War II
World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
, when European sources were not available, and
jewels were in high demand for their military applications such as for timepieces.
The process was designed primarily for the synthesis of rubies, which became the first gemstone to be produced on an industrial scale. However, the Verneuil process could also be used for the production of other stones, including
blue sapphire which required oxides of
iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
and
titanium
Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
to be used in place of chromium oxide.
The basic process can be used to form even more elaborate gemstones such as
star sapphires, where titania (
titanium dioxide
Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound derived from titanium with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or Colour Index Internationa ...
) was added and the boule was kept in the heat longer, allowing needles of
rutile
Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite.
Rutile has one of the highest refractive indices at vis ...
to crystallise within it. In 1947, the
Linde Air Products division of
Union Carbide pioneered the use of the Verneuil process for creating such star sapphires, until production was discontinued in 1974 owing to overseas competition.
Despite some improvements in the method, the Verneuil process remains virtually unchanged to this day, while maintaining a leading position in the manufacture of synthetic corundum and
spinel
Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , a diminutive form of ''spine,'' in reference to its pointed crystals.
Prop ...
gemstones. Its most significant setback came in 1917, when
Jan Czochralski
Jan Czochralski (; 23 October 1885 – 22 April 1953) was a Polish chemist who invented the Czochralski method, which is used for growing single crystals and in the production of semiconductor wafers. It is still used in over 90 percent of all ...
introduced the
Czochralski process
The Czochralski method, also Czochralski technique or Czochralski process, is a method of crystal growth used to obtain single crystals (monocrystals) of semiconductors (e.g. silicon, germanium and gallium arsenide), metals (e.g. palladium, plati ...
, which has found numerous applications in the
semiconductor industry
The semiconductor industry is the aggregate of companies engaged in the design and fabrication of semiconductors and semiconductor devices, such as transistors and integrated circuits. Its roots can be traced to the invention of the transistor ...
, where a much higher quality of crystals is required than the Verneuil process can produce. Other alternatives to the process emerged in 1957, when
Bell Labs
Nokia Bell Labs, commonly referred to as ''Bell Labs'', is an American industrial research and development company owned by Finnish technology company Nokia. With headquarters located in Murray Hill, New Jersey, Murray Hill, New Jersey, the compa ...
introduced the
hydrothermal process, and in 1958, when
Carroll Chatham
Carroll Chatham (1914–1983) was an American chemist who developed the flux method for synthesizing emeralds. He was the first person to develop a method for creating man-made emeralds that was able to make them commercially available. He founded ...
introduced the
flux method. In 1989 Larry P Kelley of ICT, Inc. also developed a variant of the Czochralski process where natural ruby is used as the 'feed' material.
Process
One of the most crucial factors in successfully crystallising an artificial gemstone is obtaining highly pure starting material, with at least 99.9995% purity.
In the case of manufacturing rubies, sapphires or
padparadscha, this material is alumina. The presence of
sodium
Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...
impurities is especially undesirable, as it makes the crystal
opaque.
But because the
bauxite
Bauxite () is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium. Bauxite consists mostly of the aluminium minerals gibbsite (), boehmite (γ-AlO(OH)), and diaspore (α-AlO(OH) ...
from which alumina is obtained is most likely by way of the
Bayer process
The Bayer process is the principal industrial means of refining bauxite to produce alumina (aluminium oxide) and was developed by Carl Josef Bayer. Bauxite, the most important ore of aluminium, contains only 30–60% aluminium oxide (Al2O3), the ...
(the first stage of which introduces
caustic soda in order to separate the Al
2O
3) particular attention must be paid to the feedstock.
Depending on the desired colouration of the crystal, small quantities of various
oxide
An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...
s are added, such as chromium oxide for a red ruby, or ferric oxide and titania for a blue sapphire. Other starting materials include titania for producing rutile, or titanyl double
oxalate
Oxalate (systematic IUPAC name: ethanedioate) is an anion with the chemical formula . This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (), and several esters such as ...
for producing strontium titanate. Alternatively, small, valueless crystals of the desired product can be used.
This starting material is finely powdered, and placed in a container within a Verneuil furnace, with an opening at the bottom through which the powder can escape when the container is vibrated. While the powder is being released,
oxygen
Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
is supplied into the furnace, and travels with the powder down a narrow tube. This tube is located within a larger tube, into which
hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
is supplied. At the point where the narrow tube opens into the larger one,
combustion
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion ...
occurs, with a flame of at least at its core. As the powder passes through the flame, it melts into small droplets, which fall onto an earthen support rod placed below. The droplets gradually form a
sinter cone on the rod, the tip of which is close enough to the core to remain liquid. It is at that tip that the
seed crystal
A seed crystal is a small piece of single crystal or polycrystal material from which a large crystal of typically the same material is grown in a laboratory. Used to replicate material, the use of seed crystal to promote growth avoids the otherwi ...
eventually forms. As more droplets fall onto the tip, a
single crystal
In materials science, a single crystal (or single-crystal solid or monocrystalline solid) is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no Grain boundary, grain bound ...
, called a ''
boule'', starts to form, and the support is slowly moved downward, allowing the base of the boule to crystallise, while its cap always remains liquid. The boule is formed in the shape of a tapered cylinder, with a diameter broadening away from the base and eventually remaining more or less constant. With a constant supply of powder and withdrawal of the support, very long cylindrical boules can be obtained. Once removed from the furnace and allowed to cool, the boule is split along its vertical axis to relieve internal pressure, otherwise the crystal will be prone to fracture when the stalk is broken due to a vertical
parting plane.
When initially outlining the process, Verneuil specified a number of conditions crucial for good results. These include: a flame temperature that is not higher than necessary for fusion; always keeping the melted product in the same part of the oxyhydrogen flame; and reducing the point of contact between the melted product and support to as small an area as possible. The average commercially produced boule using the process is in diameter and long, weighing about . The process can also be performed with a custom-oriented seed crystal to achieve a specific desired
crystallographic orientation.

Crystals produced by the Verneuil process are chemically and physically equivalent to their naturally occurring counterparts, and strong magnification is usually required to distinguish between the two. A telltale characteristic is the Verneuil crystal is curved growth lines (curved striae) form,
as the cylindrical boule grows upwards in an environment with a high
thermal gradient, while the equivalent lines in natural crystals are straight. Another distinguishing feature is the common presence of microscopic gas bubbles formed due to an excess of oxygen in the furnace; imperfections in natural crystals are usually solid impurities.
[
]
See also
* Bridgman–Stockbarger method
* Czochralski method
* Float-zone silicon
* Kyropoulos method
The Kyropoulos method, also known as the KY method or Kyropoulos technique, is a method of bulk crystal growth used to obtain single crystals.
The largest application of the Kyropoulos method is to grow large boules of single crystal sapphire u ...
* Laser-heated pedestal growth
Laser-heated pedestal growth (LHPG) or laser floating zone (LFZ) is a crystal growth technique. A narrow region of a crystal is melted with a powerful Carbon-dioxide laser, CO2 or Nd:YAG laser. The laser and hence the zone melting, floating zone, i ...
* Micro-pulling-down
* Shelby Gem Factory
The Shelby Gem Factory was the production facility of ICT Incorporated, a company in Shelby, Oceana County, Michigan, Shelby, Michigan, United States, that manufactured artificial gemstones through proprietary processes. ICT began operations in ...
References
*
*
*
*
*{{cite journal, first=D. , last=Imel , url=http://www.rochesterlapidary.org/RockCollector/2005/May-2005.pdf , title=What is the procedure by which synthetic rubies are produced? , journal=The Rock Collector , volume=105 , issue=5 , date=May 2005 , pages=6–8 , url-status=dead , archiveurl=https://web.archive.org/web/20051025160459/http://www.rochesterlapidary.org/RockCollector/2005/May-2005.pdf , archivedate=October 25, 2005
* R. T. Liddicoat Jr.
Gem
McGraw-Hill AccessScience, January 2002, Page 2.
Chemical processes
Mineralogy
Gemology
French inventions
Industrial processes
Crystals
Science and technology in France
Methods of crystal growth