Program Speaker: Paul Hlava

The Synthesis of Gemstones

by Nancy L. Attaway

Paul Hlava announced that Doug Irving, scheduled for tonight’s speaking engagement, was out of the country on a commercial geology venture and would be re-scheduled for the March meeting. In his place, Paul Hlava presented a new and informative talk, “The Synthesis of Gemstones”.

Paul began his presentation with a few introductory comments. He stated that the first synthetic gems were rubies produced in 1837. The mass production of synthetic rubies began in earnest in 1902. The first synthetic diamonds were produced in 1953 by ASEA, the Swedish Electric Company. The yearly US production of synthetic diamonds is 150 tons, mainly for industrial application.

Paul said that the concept of synthesizing gemstones is really very old. It was even fairly common in Pliny’s time. A quote from Pliny states, “I have in my library certain books by authors now living, whom I would under no circumstances name, wherein there are descriptions as to how to give the color of smaragdus (emerald) to crystallus (rock crystal) and how to imitate other transparent gems: for example, how to make a sardonychus (sardonyx) from a sarda (carnelian, in part sard): in a word to transform one stone into another. To tell the truth, there is no fraud or deceit in the world which yields greater gain and profit that that of counterfeiting gems.” Pliny lived from 23-79AD.

Paul introduced several definitions associated with his talk. He defined a gem as an outstanding example of its kind and a jewel as an object made of precious metal and enamel and/or gems used for ornamentation. He described a gemstone as a naturally-occurring material desirable for its beauty, valuable in its rarity, and both durable and stable enough to give lasting pleasure when worn as an ornament.

Paul further described other terms relating to his talk. He said that naturals were materials mined from the Earth. He stated that synthetics were identical to naturals but made by man in the laboratory. The term “man-made” has no natural equivalent, such as cubic zirconia or yttrium aluminum garnet. He defined simulants as any material with the wrong chemistry that exhibits physical properties masquerading as a gemstone, such as plastic and glass.

Paul said that before people knew the true composition of materials, they could only try to mimic natural gems. Many materials were lumped together as one gem, such as balas spinels and rubies. Emeralds, green sapphire, peridot, and tourmaline were all in the smaragdus group. Sapphire was the original name for lapis lazuli. Advances in the science of chemistry by the end of the 18th century revealed the constituent elements and coloring impurities of many gems and their proper proportions. Those of diamond were found in 1797, emerald in 1798, and ruby by 1800.

Trial and error associated with synthesizing gemstones with heat led to the development of potent torches and furnaces. Rubies and sapphires could be made at 2,200 degrees C or 4,000 degrees F. Diamonds require about 1,600 degrees C or 2,900 degrees F. The importance of pressure in making diamonds was not fully realized until recently. Diamonds require about 60,000 atmospheres of pressure. Other key ingredients necessitate the use of pure starting materials for gem synthesis, like ruby from alum.

Kurt Nassau lists over two dozen people who worked on ruby synthesis in the early 1800’s. Gaudin in 1837 was the first to make rubies using a torch, alum, corundum, and salt to make rubies. However, he thought that he had made glass, since the pieces were cloudy and showed a low specific gravity. Subsequent investigations into his procedures revealed that he actually did synthesize rubies. Fremy in 1877 used large crucibles with lead oxide flux. He made small but commercial-quality rubies. His method was deemed too expensive to compete with natural rubies.

August Verneuil, a student of Fremy, perfected a viable furnace to synthesize rubies, and he later did the same with sapphires somewhere between 1888 and 1891. Consequently, commercial mass production began in 1902. The technique is now called “flame fusion” or the “Verneuil process”. This process produces single crystals of both corundum and spinel, and almost any color is available, as well as colorless. Hundreds to thousands of furnaces currently produce millions of carats of synthetic gemstones every year. Costs run very low, just pennies per carat.

The Czochralski Crystal Pulling method of gem synthesis involves having a small seed on a rotating rod dipped into a pool of molten ruby. The rod is pulled up as the crystal grows. The end crystals result in very high quality material. The product from this method is more expensive, as the technique is tedious and requires an expensive iridium crucible. A variation of this method produces better quality boules of larger sizes.

Paul informed us that emerald synthesis poses more of a problem. Emeralds melt and recrystallize incongruently and recompose into other compounds before they melt, or they can also form these compounds upon cooling from a melt. The Verneuil method does not work for synthesizing emeralds. Emeralds must be crystallized from a solution.

Paul stated that the first successes of synthesizing emeralds emerged with high temperature solvents called fluxes. Platinum crucibles were used with flux and the correct chemicals to create the solutions needed. Emerald synthesis may or may not use seed crystals.

Paul listed several names credited with the first flux-grown emeralds. J. J. Ebelmen in 1848 used boric acid flux with powdered emerald, and tiny crystals formed upon cooling. Many researchers discovered that the best fluxes for emerald synthesis were Li2MoO7 with extra MoO3 and /or V2O5. I. G. Farben in 1934 synthesized emerald and called it “igmerald”, and Nacken synthesized emeralds between 1916 and 1928. Carroll Chatham is credited with the first homogeneous nucleations of emeralds. In 1935, he synthesized his first emerald crystals at age 21. In 1938, he had established repeatable and dependable techniques required for emerald synthesis. In 1939, he had trouble convincing the jewelry community that he had actually made emeralds. Gilson in 1964 used seeds with heterogeneous nucleation. It is thought that Chatham died of beryllium poisoning.
Paul related that flux growing of emeralds posed problems. Emerald synthesis from flux growth requires platinum crucibles that can be used only a few times before they must be replaced. The flux growth method also requires careful controls, lots of dependable electricity, and long times at temperature, about one year. All of these factors are expensive, making a pricey but excellent product.

History credits Humphrey Davy for growing quartz in 1822. He determined that quartz could grow from a saline solution by analyzing its fluid inclusions. Senarmont in 1851 synthesized quartz in small proportions. Giorgio Spezia in 1908 is given credit for his key work in synthesizing quartz, but he had placed his growing vessels upsidedown. Richard Nacken grew quartz for the Germans during WWII, and researchers in the US and in Britain successfully grew quartz also during WWII. A commercial process for quartz synthesis was established by 1950.

Paul described how quartz synthesis requires an alkaline (NaOH) aqueous solution, modest temperatures (just a bit over 300 degrees C), modest pressures (1700 bars), a modest temperature gradient (plus or minus 40 degrees C), and pure feed for about 33 days. Currently, millions of pounds of synthetic quartz are grown world-wide. Most are colorless, but some are smoky quartz, citrine, and amethyst.

Paul said that emeralds grow from solutions just like quartz, so we should be able to grow emeralds hydrothermally as well. Wyart and Scavinar attempted some of this work in 1957. In 1960, Lechleitner produced overgrowths on beryl that he called “emerita” and “symerald”. Between 1965 and 1970, Linde established a hydrothermal reaction process. Now, a number of companies can do this, also.

The Linde process is a hydrothermal reaction process and is similar to the flux-reaction process. The pressures needed run between 700 bars and 1,400 bars, and the temperatures required range between 500 degrees C to 600 degrees C. A strong acid solution is also necessary.

Paul related that the process of diamond synthesis differed greatly from the synthesis of other gemstones. Diamonds need more than heat to grow. They require a solvent and tremendous pressures, between 60,000 atmospheres to 70,000 atmospheres or about one million psi.

When researchers realized that diamonds originated from intense pressure rocks, the research on diamond synthesis accelerated. Many early workers claimed to have made diamonds. The most famous include: J. B. Hannay in 1880, who claimed to have made diamonds in iron tubes; F. F. H. Moissan, who also used iron rods, but made moissanite instead; and C. A. Parsons, who used a variety of methods and only made spinel. All were subsequently found to have failed at synthesizing diamonds, as the pressures used in their processes were way too low. Tales of laboratory experiments relate the many occurrences of explosions.

Regarding high pressure research associated with diamond synthesis, Paul said that the main problems stem from the need for materials that will continue to function at extreme temperature/pressure conditions. P.W. Bridgman is considered to be the father of high pressure research, and he published many papers on the subject.

One of Bridgman’s foremost problems was with his main seal that was not tight enough for conditions. Another researcher on a related team, Tracey Hall was able to create a seal that could withstand the intense pressures needed and still hold. Paul explained that while the majority of the Bridgman team used a 1,000-ton press and an older seal design, Tracey Hall was relegated to use the leaky old 400-ton press and his new seal design. Tracey Hall found success on December 16, 1954. The process was repeated by the team 12 out of 27 times during the next 15 days. An independent run by an outside team confirmed the technique on December 31, 1954.

The first researchers to actually synthesize diamonds were on a team at ASEA, the electric company of Sweden in 1953. To remain secretive, they did not publish their findings until after General Electric announced their success of synthesizing diamonds using a similar technique.

Paul explained that most synthetic diamonds are used for abrasives, and hundreds of millions of carats are produced each year for industrial applications. Each machine gets 6 to 8 runs per hour. Breakage still poses a problem.

During the production of synthetic diamonds, many small diamonds are made in just a few minutes. Big diamonds require a longer time period. Most synthetic diamonds are yellow in color, due to nitrogen contamination. Colorless diamonds are much more difficult to produce. Synthetic diamonds can be identified by their characteristic inclusions and by their particular fluorescence. CIS, GE, Sumitomo, and DeBeers are involved in diamond synthesis. Synthetic diamonds cost more than natural diamonds.

Paul stated that cubic zirconia is the king of diamond simulants. Many substitutes for diamonds have been tried, including TiO2, YAG, GGG, spinel, sapphire, and SrTiO3. Cubic zirconia has the best combination of properties that mimics a diamond and is very affordable. Many of these diamond simulants still require extremely high temperatures. Cubic zirconia is amazingly cheap, considering the exotic material and technique required for production. Cubic zirconia is also made in a wide variety of colors. Skull melting is used in making cubic zirconia, and the starting powder serves as a crucible. The skull is an open-ended cup made of copper cylinders, filled with zirconium oxide plus CaO or Y2O3. Radio frequency waves of energy melts solid zirconium chips in the core. Water-cooled copper tubes keep the outer portions from melting.

Paul concluded by saying that the sale of synthetic gems has not harmed sales of natural gems. Paul thinks that synthetic gems increase the sales of natural gems, as people still want jewelry with fine, natural gemstones. Determining the synthetic gems from their natural counterparts is difficult in some cases. Identification is usually based upon the inclusions contained. Synthetic gems have created their own niche in the gem market. Paul thinks that gems are usually not a good investment, but exceptions do exist. Also, Paul feels that disclosure is absolutely essential.

{Editor’s comment: See Dr. Joel E. Arem’s Color Encyclopedia of Gemstones for more information and illustrations of gem synthesis techniques on pages 211 to 235.}