After blue, yellow is the most sought after color in today’s sapphire market. Many yellow sapphires closely resemble yellow diamonds. They can range in color from greenish yellow and orangish yellow, to everything in between. The preferred yellow sapphire color is a medium, vibrant canary yellow. A deep, somewhat orange or brownish yellow, reminiscent of a whisky color, is highly valued in some Asian markets. Darker stones are sold as brown sapphires, not yellow, and have historically commanded lower prices although they are currently experiencing a surge in popularity and value.
There are two very different causes of yellow coloration in sapphires. The most common cause is the trace element iron. In general, increased iron concentrations will increase color saturation. Yellow sapphires can also be colored naturally by low-level radiation within the earth or by lab-induced irradiation. Although neither of these types of yellow sapphires is harmful to humans or radioactive, their color has been known to fade with exposure to heat and light. For this reason, most consumers avoid them. We test all our yellow sapphires for signs of irradiation treatment by various methods, such as exposing the gemstones to UV light.
Besides irradiation, yellow sapphires are frequently subjected to intense heat and diffusion treatments. Heat treatment transforms worthless rough into marketable gems, vastly increasing the supply of attractive yellow sapphires on the market today. Unheated yellow sapphires with strong saturation remain quite rare.
Yellow sapphires frequently have fewer inclusions than other sapphire colors, and they are held to higher clarity standards than blue, pink, or padparadscha sapphires. The trace element titanium causes an undesirable green cast in yellow sapphires, and the most valuable stones are relatively titanium-free. For this reason, titanium-bearing rutile silk is less common in fine yellow sapphires than sapphires of other colors. Yellow sapphire’s relative clarity is quite convenient, since the medium tone at which the color shows best does little to hide inclusions.
Yellow sapphire rough has traditionally been less costly than blue, pink, or padparadscha, so cutters are more reluctant to compromise brilliance in favor of weight retention. As a result, well-cut yellow sapphires are easier to find than other sapphire colors. Yellow sapphires are also more likely to be available in specialty cuts such as radiant cuts.
Read more about Origins of Sapphires