Editor’s Note
This article highlights the strong demand for colored gemstones at auction, using opals as a case study. It notes that while play-of-color is a key driver of value for many opals, the most prized varieties—fire and black opals—are exceptions to this rule.
At a recent Sotheby’s jewelry auction, various colored gemstones continued to be highly sought after, with opal, commonly known as ‘protein stone’, being one of them. A milky-white opal ring with pink and purple play-of-color started at 120,000 HKD and sold for 350,000 HKD; a red series opal necklace fetched a price exceeding one million HKD. While most opals are famous for their play-of-color, the most valuable fire opals and black opals do not exhibit this characteristic. Beginners collecting colored gemstones should not overlook these details.
In the Guangzhou market, since 2011, the sales volume of opals has shown a sharp upward trend. They are not only found in the wholesale markets of Liwan District but are also occasionally sold by jewelry retailers near Tianhe City. Their prices have also shown a rapid increase compared to previous years. Currently, a piece of opal measuring 6mm x 9mm generally retails for 10,000 to 20,000 RMB, placing it in a similar price range as sapphires found in the Guangzhou market.
On average over the past 10 years, the appreciation rate for opals has been around 10 times. A 50-carat opal rough stone that sold for around 300,000 RMB in 2001 now sells for approximately 1.5 million RMB.
The rate of price increase is roughly on par with mid-grade jadeite and rubies/sapphires, but not as high as Hetian jade, top-grade jadeite, or Shoushan stone, and certainly not as high as over-hyped gemstone varieties like Huanglong jade, Tianhuang stone, or chicken-blood stone.
Consequently, most industry insiders believe that opal is a healthily growing gemstone suitable for buying on dips.
Many mainland collectors mistakenly believe that the more colors an opal changes, the more valuable it is. However, Liang Zhanxiong, President of the Guangdong Gold & Silver Jewelry Association, explains that there are four criteria for evaluating opal: size, color, play-of-color, and hardness.
Among these four factors, color has the greatest impact on an opal’s value. Fire opals with flame-like colors are the most valuable, followed by black opals. The prices of other white, milky, or blue opals are relatively similar. Fire opals and black opals are considered high-end products within the opal category and typically do not show significant play-of-color. Their preciousness lies in their scarcity and higher degree of flatness. Therefore, an opal is not necessarily more expensive just because it displays more color changes. The more regular the color changes and the higher the degree of iridescent play-of-color, the more valuable the opal.
Furthermore, the higher the hardness of an opal, the higher its value. This is because opal is primarily composed of silica and is prone to collapse. Opals with higher hardness are less likely to collapse and have fewer flaws.
Opal counterfeiting mainly takes two forms: synthetic products and composite products.
As for composite products, they involve bonding a thin layer of opal onto an ordinary stone. For identification, it’s best to use a magnifying glass to look for bonding seams around the edges of the stone’s surface.
Opal is an amorphous, non-crystalline gemstone composed of silica. White series opals are commonly known as ‘protein stone’. With a long history, opals were already popular in the imperial courts of ancient Rome over 2000 years ago. They were introduced to China during the Ming and Qing dynasties and were reserved for imperial use. Currently, 95% of the world’s opal mines are located in Australia.
