With its palette of sky, water, earth and trees, turquoise has been traded and worked and worn throughout history and across cultures.
But what makes a good turquoise stone? The answer is not always clear.
In diamonds, the Four Cs (color, clarity, cut and carat weight) are an accepted industry standard for determining quality. In the world of faceted gemstones such as sapphires, rubies or emeralds, aspects of color — hue, tone, saturation — take center stage.
When it comes to turquoise, though, opinions tend to be all over the map — much like the mineral-rich opaque stone itself, which can be monochromatic or variegated, clear as a cloudless summer sky or laced with a spiderweb pattern of host rock, or matrix. Preferences have varied by region and change over time.
Then there is the source of the stone. Passionate collectors often seek turquoise from specific mines, many of which are no longer in production.
The scarcity of high-quality natural turquoise has been driving up prices — a rare stone from a classic mine may cost 25 to 30 times what it did 25 years ago, experts say — but there is no widely accepted standard to determine what makes one stone better than another.
That lack has created confusion and allowed misrepresentation, according to Joe Dan Lowry, 56, and his son, Jacob Lowry, 29, among the fourth and fifth generations of their family to work in turquoise. (The Lowry family owns the Turquoise Museum in Albuquerque, with Joe Dan as its curator and Jacob as its executive director.)
Without a standard, they said, it has been too easy for someone to pass off an unremarkable stone as something rare and valuable, noting that people selling such a stone might even believe it is top quality because they have seen only a limited portion of the spectrum. “There’s a difference between ‘This is the best turquoise I’ve ever seen’ and ‘This is the best turquoise that ever existed,’” Jacob said.
For five years the Lowrys have been developing a grading system that they hope will culminate in an industry standard and give gem-quality natural turquoise the respect they say it deserves.
“Turquoise, in my opinion, should be on the global stage,” said Joe Dan, the co-author with his father, Joe P. Lowry, of the 2010 book “Turquoise: The World Story of a Fascinating Gemstone” and, in 2002, “Turquoise Unearthed: An Illustrated Guide.”
The stone, he argued, is as distinctive as the people who love it and is unrivaled among other gems for its history and color. “All that is missing,” he said, “is the standard to show the world how rare it actually is and how beautiful it is, even within cultures that might not use the rarest.”
Master Stones
The Lowrys are not the first to work on turquoise grading. But what sets their effort apart, according to them and others in the field, is that they have been compiling sets of master stones to be used as benchmarks.
“This is the first real attempt to introduce rigor into the discussion about grading turquoise,” said Mark Bahti, who owns Bahti Indian Arts in Santa Fe, N.M., and Tucson, Ariz., following his father into the business more than 50 years ago. He credited the Lowrys with bringing science and common sense to a subject long considered subjective.
The Lowrys’ system considers color as the most important factor in turquoise, followed by the presence or the absence of matrix, the term for remnants of host rock often visible in the stone. Then there is the elusive quality known as “zat,” a term used more than a century ago for a kind of wow factor.
“I think the effort towards creating a grading system is very helpful and is needed.,” Mr. Bahti said.
But can it be achieved? He said he really did not have an opinion. “These guys are doing an amazing job, and I’m a spectator.”
Mike Ryan II, who has written extensively about the history of turquoise in the United States, said a Facebook group that he was involved in about a decade ago tried to develop a turquoise grading system, but it got bogged down in geology-related issues.
He said he had suggested some grading rules based on a system proposed in the 1970s, but the group rejected them. He ended up posting those rules on his own and made a series of YouTube videos on the subject.
While he does not agree with every detail of the Lowrys’ approach, which Joe Dan introduced at a conference in Albuquerque two years ago, Mr. Ryan said he thought the master sets were an important step. “What he has done using the actual stones, I think that’s tremendous,” he said.
Au Naturel
Turquoise is found in certain arid terrains where groundwater has seeped into crevices, depositing a mix of minerals over time. The result of this slow, sedimentary process is what the Gemological Institute of America (G.I.A.) has described as “a porous, semitranslucent to opaque compound of hydrated copper and aluminum phosphate.”
The stone has been mined for thousands of years and used for adornment by many civilizations, including the Egyptian, Persian, Chinese, Tibetan, Incan, Mesoamerican and Southwest Native American cultures, Mr. Lowry and his father wrote in their 2010 book. Many experts have said that the word turquoise, from the French word for Turkish, alludes to the Turkish traders thought to have introduced the distinctive blue Persian variety of the stone to France in the 13th century.
In its softest form, turquoise is chalky; it hardens and picks up richer colors as more minerals are accumulated during its formation. On the Mohs scale, used to measure gem and mineral hardness, turquoise ranks from five to six, compared with 10 for diamond.
Much of the turquoise sold today has been treated in some way to improve the color or make it more usable in jewelry.
The Lowrys said their proposed grading system, at least initially, would focus only on natural, untreated turquoise. “You can’t start with the imitations,” Jacob said. “You have to grade what they’re imitating.”
And if history is any indicator, it is not surprising that their grading system is taking time to evolve. The G.I.A., which has issued diamond grading reports since 1953, spent about a decade working out that system, according to Tom Moses, its executive vice president and chief laboratory and research officer.
The G.I.A. does not grade turquoise or see many examples of it in its laboratories, Mr. Moses said, though occasionally it will be asked to identify whether a stone is in fact turquoise and whether it has been treated. “It’s kind of tough at times to figure out what’s been done to it,” he said.
Tangible Turquoise
In the entryway to the Turquoise Museum, long strands of tiny turquoise stones and crystals cascade from the high ceiling like a glittery waterfall. One morning before the museum opened, Joe Dan and Jacob brought out the 24 master sets related to color, matrix and zat, totaling 192 stones, that they have assembled over the years.
The small case of blue turquoise, for example, held 14 cut and polished stones of different sizes and from different countries, ranging from a pale tint to a deep ocean hue. Other cases contained light-to-intense selections of green, green-blue and blue-green.
Their idea is that someone could compare a turquoise to the set with the closest hues, to see where it places in terms of depth and brilliance of color. The same process would then be followed with the sets of stones showing common-to-rare styles of matrix or clarity, as well as zat.
Once a stone had a numerical score based on these criteria — with points off for flaws — a grader would make note of other factors that do not affect grade, but might affect value, such as cut, carat weight and provenance. (In addition to the primary 24 sets of stones, the Lowrys have more than 30 sets to show the potential quality and rarity of stones from mines around the world, including the American Southwest, China, Iran, Egypt, Mexico and Chile.) But they stressed their system was designed to assess grade, not price.
The master stones show the range of natural turquoise in a way that is tangible and can be taught, Joe Dan said. “Unless you have all of the stones to prove and be corrected from,” he said, “then all you have is a mental exercise.”
The idea of master stones is not new; many laboratories that grade diamonds and other gems have such tools. Stuart Robertson, the president of Gemworld International in Glenview, Ill., said it used ruby and sapphire master sets for classes on colored stone grading. (It also has created a comparison book, “World of Color,” with representations of 1,400 colors.)
The Lowrys acknowledged that they had yet to determine how their master stone sets could be replicated or the grading system disseminated. Photography may be one possibility, they said, and artificial intelligence, another.
They also said they did not know how the system might ultimately be managed. But they were adamant that it would not bear their family name or that of the museum, and that their master stones would be used solely for grading.
“None of these stones, and there are some very expensive stones in here, are ever going to be sold,” Joe Dan said.
Peer Review
The Lowrys said they had asked a few experts to visit Albuquerque to score an ever-increasing number of samples against the master sets in a kind of peer review of their system, which they hoped to finish by 2026. They said they needed to determine whether the grading would be consistent and whether the master sets should be altered or have gaps.
Maureen Pratt, a gemologist and appraiser in Los Angeles who is participating in the process, said she believed a grading system could help appraisers evaluate stones in situations such as insurance assessments or to determine the value of a donation or an estate. “Having a common language of grading is really important,” she said.
And Dye Masaki of Tokyo, who began collecting turquoise in 1989 and also is involved in the testing, said it might take many years for the system to be finalized, but it would be an important legacy.
“Not many people know about turquoise,” he said in a phone interview from Flagstaff, Ariz., where he was on one of his twice-yearly visits to the American Southwest. Through his shop in Tokyo, called Native Spirit, he sells high-end Native American jewelry and educates his customers about the stone.
“To obtain rare turquoise, it takes time, effort and reliable connections, and it is not easy for everyone to do it,” he said.
An Art Stone
Not everyone in the turquoise trade is convinced of the need for a grading system.
In a joint video interview with Mr. Ryan, his co-author on two books about turquoise, Philip Chambless called himself a “doubting Thomas” on the subject.
The longtime turquoise miner said he wondered whether a grading scale would make it harder for him to sell the commercial-grade turquoise that had covered the everyday costs of his mining operations. Still, he said, he could understand the appeal at the higher end.
“If a person paid $10,000 for a stone, that person would probably want to know how that stone graded out,” he said, speaking from Esmeralda County, Nev., where he and his business partners were working turquoise and other mining claims.
Mr. Chambless also said turquoise’s value as an “art stone” should not be overlooked. “It’s the love affair with the stone,” he said, rather than a numeric grade.
George Rivera, a Native American artist who has used natural turquoise in some of his sculptural jewelry, said he had paid as much as five figures for rare stones and had sometimes even paid in installments, trusting in “the quality of the stone and in my art” that it would be a good investment.
The enthusiasm of his buyers has proved his point, he said.
Mr. Rivera, a former governor of Pojoaque Pueblo, in northern New Mexico, said turquoise was especially meaningful to him and many other artists in the Southwest “because it’s from the ground where we live.”
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