Ruby and sapphire are two “blood brothers” in the corundum family. One is hot and wayward, the other is cold and calm. The temperament of the former is controlled by an element called chromium. Thanks to this, the stone gains its value and radiates natural fluorescence, which literally highlights the ruby from the inside.
In its primary form, the color of almost all rubies is a dark crimson. The ace has a clean, bright, strongly fluorescent red color of such high intensity. Any deviation in the direction of orange or yellow hues are undesirable — they are caused by the invasion of the structure of the stone by “uninvited guests.” For example, trivalent iron reduces the fluorescence of the crystal and adds a brownish tinge, that’s why Thai corundums often look more like garnets. Ideally, the crystal should be neither too dark nor too light. In the first case the brightness of the mineral is affected, and in the second one it simply turns into a pink sapphire. To tell the truth, the line between a ruby and pink sapphire is very thin, since pink is part of the red spectrum. Therefore, in most cases, the “pedigree” of the mineral depends on the personal perception of the appraiser-gemologist.
“Pigeon’s blood” rubies
Earlier the “pigeon blood” term applied only to the stones of the highest color category from Burmese mines. But over time it has expanded in geography. For example, at the end of 2016, the Swiss laboratory Gübelin appropriated its ruby from Afghanistan.
In fact, “Burmese rubies” are nothing more than a much-touted brand name, such as “Colombian emeralds” or “Golconda diamonds”. In absolutely any mining location both the highest quality stones and completely unsuitable ones for jewelry can be found. Yet none of the sources can be a guarantor. All three of the above-mentioned deposits (Burma, Colombia, and Golconda) were the first known sources of high-end minerals. Thus other mines that have been discovered relatively recently will only be able to compete with the popularity of old ones after but a few centuries.
Ruby inclusions and treatment
Almost all rubies have inclusions, the size and location of which affect the transparency, gloss and value of the stone, as well as its durability. The exception can be attributed only to a barely noticeable presence of the finest needles of rutile (a light “silk effect”) — such corundum acquires a very beautiful soft velvety color, while remaining transparent. But if there is too much rutile the crystal becomes cloudy and less attractive.
The vast majority of this category of corundum ennobles by heat treatment, as well as by filling the cracks with glass. When the crystal is heated to 800-1200 degrees Celsius, an unwanted bluish tint disappears, and when the temperature rises to 1400-1800 degrees, the rutile needles “break” and become almost invisible. In the process of calcination, various elements are added to the furnace, which contribute to the ruby purity improvement. Subjected to a similar treatment, these minerals always look cleaner and more intense than they were originally. But the cost will be much cheaper than that of their untreated counterparts.
It is important to note that over 99% of all rubies available on the jewelry market are ennobled. The number of stones that have not undergone any treatment that are clean, bright and saturated, can only be measured as a few thousand pieces.
Before giving the stone its shape and faceting, the specialist carefully studies it. When it comes to the highest quality rubies, a cutter’s error can cost hundreds of thousands of dollars. It is important to study the structure of the stone, the nature of its inclusions and the distribution of color, and only then can they start cutting.
Like most gemstones, ruby has pleochroism. This is the appearance of different tints of color in the crystal. Thus from one side it can appear purple-red, while from the other it could be more of an orange-red. The cutter’s task is to minimize the orange tint. Instead they try to make the color of the stone as close to the “pigeon blood” color as possible. However, experts are almost always striving to keep the maximum weight of the stone. This is the reason why they usually prefer to sacrifice the purity and color for the sake of carat weight.
The cut is very important for the final cost. The most expensive and practically “elusive” cut is a rectangular one (like an “emerald”, for example). The fact is that this form is not so effective in making the color richer than the “oval” or “cushion” cuts (which are the most popular ones). And if the “cushion” is able to give a “pigeon blood” color, the same stone in the emerald cut will simply be “red intense”. In order to achieve such a rare and beautiful form the stone must be just perfect. Not surprisingly, the price of a rectangular cut ruby may be 50% more expensive than the same stone in another shape.
The influence of a ruby’s weight on its value
Size always matters! For example, the cost per carat for a 5 cts ruby can be ten times higher than a 1 ct stone with similar characteristics. A top stone’s price may be measured in millions. For example, in May 2015 the Sotheby’s auction set a new world record for the precious red corundum, selling a ring with 25.59 cts of ruby for $32.4 million, working out to more than $1.2 million per carat.
In the ruby crystal, hundreds of different shades of red, brown, orange and even blue can appear, and they can’t be grouped in one common evaluation system. As a result many gemological labs invent their own terms and designations. For example, the Swiss GRS contrived the “type pigeon blood”, which marks a large number of stones which have nothing in common with the highest category of ruby color. This is not a fraud, but a commercial trick, which many beginner-collectors fall for. That’s why for many jewelry companies “pigeon blood” corundum is not a rarity.
The most objective conclusions for assessing rubies come from Swiss Gübelin and SSEF labs, while American AGL or GIA are also considered as authoritative figures. As for the GRS reports, they are mainly needed by those who want to sell the stone, as the ruby testing system, invented by this company, sounds more pleasant and attractive for the less savvy buyers. However, when it comes to minerals of exceptional quality and color, the seller will try to get as many certificates as possible (there should be a minimum of two), confirming the origin of the stone (determined by the chemical composition), as well as its unique characteristics. For example, the aforementioned ruby record-holder at the Sotheby’s auction provided two reports — from SSEF and Gübelin.