Creation plays by very frustrating rules when it comes to pure red and orange diamonds. Yet with nearly 100 million carats of diamond mined annually, collectors of fancy colors still feel good reason to hope for a handful of stones with these two rarest of shades. So while the search for pure orange diamonds is like looking for a needle in a haystack, it is child’s play next to the grail-quest for pure red diamonds.
Nature is sporting enough to provide encouraging numbers of fancy color diamonds with golden amber and fiery autumn hues, but the orange in these stones usually amounts to a secondary tinge or color highlight. Collectors lucky enough to own the occasional orange stone whose hue truly conjures pumpkin or cantaloupe know they possess one of the world’s rarest diamond treasures. There are just enough of these stones to nourish dreams of owning one. But reality nearly always falls far short of fantasy. “I’ve seen a dozen diamonds that were certified as pure orange,” says fancy color diamond specialist Alan Bronstein, Aurora Gems, New York. “Unfortunately, only three faced up with decent color. The others were too washed out.”
So close and yet so far
To bolster orange in diamonds, nature endows most with brown. This blending is variously described as “burnt orange,” “cognac” and “copper” in the trade.
The lopsided ratio between pure-orange and brown-orange diamonds widens in the laboratory where since the late 1940s treaters have been roasting diamonds to sizzling shades of fancy intense yellow and burnt orange via a two-step process of high-energy irradiation followed by high-temperature heat. Yet after more than 40 years, diamond-colorizing adepts still haven’t found a way to regularly induce pure orange pigments. Producing subtle colors reminiscent of cantaloupe remains as elusive as ever.
Hence rarity second only to that of true-red diamonds makes the 2.10-carat pure orange stone in the 250-specimen Aurora colored diamond collection on display at New York’s American Museum of Natural History one of a kind. The Gemological Institute of America Laboratory paid this stone the highest praise possible for is hue by grading it “fancy orange.” GIA rarely allows a diamond to leave its lab with this designation. Here’s why.
Into the Green
There are many orangy but almost no orange diamonds in the marketplace. Pure orange, it seems, is a lot, maybe too much, to ask of the color chemistry and mechanics that govern diamonds. “Never forget,” urges gemologist and fancy diamond specialist Stephen Hofer, “that orange is a hybrid in the truest sense, between yellow and red. So it’s par for the course to see strong modifiers in orange diamonds.”
To understand why orange in diamonds is usually a mixture of hues, you must understand the causes of color in this gem. The diamond’s crystal lattice, composed of tightly bonded carbon atoms, makes this gem ultra-resistant to infiltration by impurity atoms. Nevertheless, atoms of two kinds often penetrate in sufficient quantities to act as coloring agents: nitrogen, the primary cause of yellow and orange, as well as boron, the primary cause of blue. But for every diamond blued by boron, a million are yellowed by nitrogen. Bluing and yellowing are usually slight rather than strong—so slight that color is generally masked by the diamond’s bleaching brilliance. However, a certain percentage of stones still qualify as colored diamonds.