LONDON, United Kingdom — In 1946, while working on the De Beers account for the New York agency N.W. Ayer & Son, copywriter Frances Gerety came up with what would be one of the most enduring advertising slogans of the century. The tagline she delivered to the powerful diamond mining and trading cartel — 'A Diamond is Forever' — indelibly linked the gemstones to marriage proposals and quickly took on the weight of authority, helping to ensure that diamonds would dominate the fine jewellery market for the latter half of the twentieth century.

But over the last few years, the sea of sparkling ice has, little by little, become enlivened by splashes of colour, as a number of factors push coloured stones — everything from emeralds, rubies and sapphires to turquoise, lapis and coral — back into vogue.

“Coloured stones were one of the key elements of high jewellery, historically,” Nicolas Bos, CEO and creative director of Van Cleef & Arpels, told BoF. “Mostly because of their expertise,” he continued. “For generations houses such as ours had in-house experts searching for the stones and guaranteeing their quality. For Van Cleef & Arpels, it was one of the qualities of the house to provide and work with exceptional gemstones. It never disappeared — but that tradition somehow diminished. By the 1980s and 90s, high jewellery became more conservative in design,” he added. But in the last decade or so, Bos has seen “a comeback of creativity in high jewellery” in which the return of colour has played a key part. “There’s only so much that you can do with white diamonds and simple settings at the end of the day,” he said. The house now includes coloured stones in its themed collections, such as L’Atlantide or Les Voyage Extraordinaire — “not only precious but also semi-precious and fine stones that were very important in fine jewellery 80 years ago and had completely disappeared in the 1980s and 90s.”

The fall and return to favour of coloured stones is about more than shifting fashions, however. Since the mid-twentieth century, the rising reputation of diamonds was boosted incalculably by the major marketing machine of De Beers (Matthew Hart's Diamond: the History of a Cold Blooded Love Affair, published in 2002, estimated De Beers annual advertising budget at $200 million).

While, today, De Beers operates a 50/50 joint retail venture with LVMH, targeting consumers directly, the company — historically, mine-owners and distributers — has long been engaged in promoting the underlying social constructs that underpin the diamond market, rather than any product line in particular, seeding the notion of, for example, how much a man should spend on an engagement ring (‘Isn’t she worth two month’s salary?’), diamonds as markers of a significant event (‘Which Millennium are you waiting for?’) or the purchasing of jewellery by women for themselves as an empowering act (‘Women of the world, raise your right hand’).

Significantly, De Beers also developed a set of criteria for evaluating diamonds in order to support the idea that the stones had intrinsic value that could be objectively established, which helped to build consumer confidence. The system was known as the ‘4C’s’ — colour, cut, clarity and carats. Price, supply and quality have also been relatively predictable for jewellers working with the stones, not least because De Beers, at the height of its power, controlled some 80 percent of the world’s rough diamond market.

But while De Beers provided a unifying force behind the sourcing and promotion of diamonds, coloured gemstones, rarer and more geologically diverse, have historically been mined by smaller, independent outfits. Neither has there been a universal grading system like the 4C’s, meaning consumer confidence was based almost entirely on the relationships between jewellers and customers.

This bond of trust was deeply shaken in the late 1990s by a series of ‘exposés’ that appeared on US television, knocking jewellers for not disclosing treatments such as oiling and filling that had been applied to gemstones prior to sale. While many of these were traditional and accepted techniques, the suggestion of dubious practices had a huge impact. “Around 2000, it was extremely difficult to sell important coloured stones,” said Bos. “The most conservative approach was to stay out of it and go for something else.”

But in recent years, consumer confidence in coloured stones has been rebuilt, thanks, in part, to tighter guidelines regarding the disclosure of gemstone treatments. In April 2001, the US Federal Trade Commission updated its guidelines, compelling jewellers to disclose treatments that might affect a stone’s value that were impermanent or that might have required the stone to be cared for in a special way. But for jewellery houses, inconsistent supply and pricing were still an issue.

"Gemstone supply was very inconsistent, because it was traditionally local people bringing up what they could find," explained Gabriella Harvey, director of cut and polished stones for the London-based gemstone company Gemfields. "It was difficult for companies to plan ahead. If a big company like Tiffany & Co had one beautiful stone they wouldn't know if they'd find another and how much it would cost. Back in the day, it could take seven years to build up a line of matching emeralds."

To consumers, Gemfields promotes itself as a source of ethically mined gems. But within the industry, its biggest impact has been the development of the first formal grading system for coloured stones. “We’ve developed a grading system for rough emeralds and rubies with 400 different grades covering colour, clarity, weight and so on. The grades are consistent across auctions and, because of this, jewellers will know that they can do, for example, matching pairs. It is helping bring gemstones back because it’s more consistent,” explained Harvey. “You can walk down Bond Street or Madison Avenue and there’s so much more colour now in the jewellery shop windows and that’s because people can plan ahead. A grade ‘A’ will be a grade ‘A’ for ever.”

Gemfields runs auctions four times a year. At the company’s auction of high quality emerald and beryl, held in Lusaka, Zambia in February of this year, 0.62 million carats were sold for $36.5 million. The fifteen auctions held by the company since 2009 have seen a consistent rise in price per carat, quality being equal.

While consistency of supply and pricing has made it easier for major jewellery houses to include coloured stones in their collections, there has also been a growing international demand from consumers. “Asia has been leading the way when it comes to demand for coloured stones,” explained Prateek Nigam, director of the Jaipur, India-based Oriental Gem Co which uses coloured stones in 80 percent of its jewellery designs. “There is a huge demand for exotic stones right now; people are more aware that some of these stones are 1,000 times more rare than diamonds.”

Oriental Gem Co.’s gemstone-based designs retail from as low as $500 to over $400,000. The company currently has 288 points of sale in over 40 countries around the world. “Each territory has a certain taste and appetite,” said Nigam. “Factors such as the demographics, trends and perceived intrinsic value play a big role in determining which stones might do very well. Opals are a big trend in Europe, America and Asia, but they just don’t sell well in Brazil where there are considered unlucky. Tourmalines are high in demand in Asia, but in the Americas they just don’t understand why the stone is so expensive.”

Lesley Schiff, founder of the Talisman jewellery gallery based in London’s Harvey Nichols store has worked in the jewellery trade for over 40 years now and is a leading specialist in contemporary studio jewellery. She has sensed a definite shift towards colour in recent years, and is now seeing a second wave of impact. “The price of coloured stones has hugely increased — tourmalines are astronomically priced. Many jewellers are now looking at stones they haven’t used before, such as organic stones like rutilated quartz. They’re looking for stones with a lot of character rather than trusting conventional semi-precious stones; turquoise and chrysoprase are really sought after again. The stones that were used, for example in important pieces by Bulgari in the 1950s, 60s and 70s — lapis, turquoise, corals, chrysoprase — fell out of fashion. Now fashion has changed and they’re coming back.”

Pieces at Talisman range in price from £30 to £50,000 (about $50 to $84,000) with a “sweet spot,” identified by Schiff, of around £1,000-£5,000 for women making an immediate purchase for themselves. “Women who might have bought bold costume jewellery a few years ago will now pay more because there’s now good bold fine jewellery available that almost has a costume-y look to it.”

Like many store-based jewellers, Schiff is wary of the growing online market for diamond jewellery. In recent years, e-tailers have attracted consumers by offering pricing that is both more transparent and lower, undercutting brick-and-mortar jewellers. Blue Nile posted first quarter net income for 2014 at $103.7 million. And the idea of competitive pricing, lower margins and bargains, sits uneasily with the idea of diamonds as the ultimate luxury purchase. “The image of diamonds is changing,” said Schiff. “Maybe because everyone can buy a hot diamond piece with a little stone.”

"Diamonds are easier to find. You don't have to see them in person. Coloured gemstones have so much more personality," said Michelle Graff, editor-in-chief of the New York-based National Jeweller. Visiting jewellery shows and events around the world, Graff has an overview of industry trends and has noted the growing interest in coloured stones. In part, she also attributes this to adoption amongst highly influential global celebrities and the increasing presence of coloured stones on the red carpet. (Kate Middleton, for example, wore a sapphire engagement ring).

Graff also sees another key driver in the rise of millennial consumers: “The younger generations don’t hold diamonds in the same esteem as their predecessors — they’re looking for something different from what their friends have. With the baby boomers it was all about keeping up with the Joneses. For the Millennials, it’s about having something different and more personal — and coloured gemstones give more variety.”

Disclosure: The author contributed the introduction to Thames & Hudson's Emerald, the publication of which was supported by Gemfields.