The ruby is one among four of the most expensive gemstones in the world, along with the diamond, the emerald and the sapphire. Having said this, the latter is its “blood” relative. Both minerals are corundum and differ only in color. But what makes the ruby so valuable and desirable?
«Pigeon’s blood» ruby
Pure corundum is completely colorless. But if a tiny particle of chromium gets into it the stone turns red. The ace ruby has a clean, bright, strongly fluorescent red color of such high intensity. Any deviation in the direction of the orange or purple tints is undesirable. It significantly reduces the cost of the stone. The ruby 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. But where is that invisible boundary of color held, as in fact, pink is a part of the red spectrum? In most cases, everything depends on the personal perception of the appraiser-gemologist.
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. 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 the 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 India’s 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.
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. That is why the vast majority of this category of corundum ennobles by heat treatment, as well as by filling the voids with glass. 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 their untreated counterpart.
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. It is for this reason that most people are not in a position to not only buy them, but even just see them.
Before giving the stone 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 inclusion 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 the other one 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 (for example, an “emerald”). 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, or more than $1.2 million per carat.
Not an experienced gemologist? Understanding all the nuances mentioned above is a very difficult task. For this reason it’s important to buy stones only from reliable sellers. And if you have any doubt — always ask for a certificate. 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. However, in a gemological examination there is also a laboratory whose conclusion is at least not serious for the goal of a purchase or sale transactions of rubies. The Swiss GRS often overstate the characteristics of these kinds of corundum for the sake of regular clients, and release more “pigeon blood” rubies than the other four laboratories combined.
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.