Natural sapphire is most often a translucent layered and fissured mineral of all kinds of shades of all colors of the rainbow. It happens to him to be colorless. Is it easy to get jewelry-grade sapphire? It is very difficult: the high hardness of the mineral, its unacceptability to geometric deformations causes a violation of the integrity of the crystals.
Intracrystalline impurities, which give the effect of mineral discoloration, are often concentrated unevenly in the stone. Filling cracks with foreign solutions and melts turns the initially monolithic formations of corundum (the technical name of sapphires and rubies) when in warehouses and when in dumps of pollution.
That is why the lion’s share of sapphires entering the healing crystal jewelry market is being ennobled.
Today, sapphire ennoblement techniques are plentiful and cunning. Old masters of Sri Lanka, a recognized center for the extraction of blue stones, use the thermal method of thickening color.
By nature, Sri Lankan sapphires are for the most part weakly colored, and not too similar to the sparkling insets in rings and earrings. Called the term “geuda”, these stones do not have any serious initial price. However, a high-temperature refinement turns geuda into a real blue sapphire.
The islanders are not worried if suddenly overheating of the harvested material occurs. Corundums, heated to 1300 and even to 1400 ° C, acquire the effect of asterism. They are polished with cabochons so that six-pointed stars play brighter on the surface of the stone.
Red corundums, or rubies, are often quite noticeably bluish initially. Especially strongly, such a defect spoils beautiful pink stones. Heating in an acidic environment to 800 ° C helps get rid of unnecessary blue.
This method applies to excessively dark blue sapphires. It’s only an emerald, the thicker the color, the more expensive. The traces of such refinement of sapphires are almost indistinguishable during the usual inspection of the stone, which allows the modified crystals to enter the jewelry shops under the guise of completely natural raw materials.
The scourge of natural corundum is fracturing. In order to “heal” deaf and cracking cracks, the craftsmen have to go to tricks. Sometimes it turns out to be an effective method of heating the stone in an aluminum oxide environment. Do not forget that in its chemical essence corundum is aluminum oxide Al2O3. The molten substance can penetrate into cracks and cement them better than any glue.
True, a colorless glassy material (the so-called leucosapphire), obtained as a result of this manipulation and filling the microscopic cavities in the stone, is detected using an electron microscope. Nevertheless, the jewelry quality of sapphires “cured” in this way is much higher than the quality of crystals ennobled with oil, resin or wax.
Experts do not see much difference in the quality of sapphires, the cracks of which were filled with molten silicates of a particular variety. This method of ennoblement of sapphires, having come to replace the ancient oil-wax baths in the already distant past, can be used today.
Entered into jewelry technology in the mid-twentieth century, epoxy gives about the same visual effect as glass cements in sapphire cracks. A ray of light, refracting at the boundaries of media alien to corundum materials, flashes with bright sparks from deep purple to bright pink.
The impregnation of corundum with substances actively diffusing into the outer layers of the mineral, and thus changing the natural color of the stone, is especially often used to enrich red and blue sapphires. Often, the color improvement achieved in this way occurs with a simultaneous decrease in gloss – which is unacceptable for gem-quality stones.
The transformation of inexpressive weak-pink sapphires into bright orange stones is due to thermal diffusion impregnation of corundum with beryllium. Due to the small atomic mass, beryllium penetrates deep into the crystal body of sapphire quite deeply: corundum jewelry inserts up to 3 millimeters in size can be saturated with beryllium over the entire thickness of the stone.
The enrichment of sapphires with beryllium is much less attractive if the crystal is large and beryllium forms only a faded layer on the surface of the stone.
Without denying the effectiveness of thermal diffusion treatment of corundum, modern gemology requires the obligatory indication of the fact of applying the method to certification of finished products. The expression beryllium treated in the document means the saturation of corundum with beryllium ions in order to obtain warm shades of color.
By nature, yellowish or slightly pinkish sapphires after beryllium treated become beautiful gems of yellow and orange. But the expression diffusion is more often used to document the “turning blue” of the stone. The diffusion method introduces iron and vanadium ions into the thickness of the gem, causing a change in the throughput of the crystal lattice regarding electromagnetic radiation of the visible spectrum.
However, specialists even without certificates distinguish corundum’s that have undergone thermal diffusion treatment. Since diffusion does not affect the central volume of the stone, a small volume of a natural-colored crystal always remains in the middle of a gem of a sufficiently large size. Special filters mounted on the microscope lens allow you to confidently determine the initial color of the mineral.
Substances that diffuse deep into the stone do not change the nature of sapphire too much. The glass transition of a mineral is another matter. To refine red corundums (rubies), the led-glass filling method is used, or the voids in the stone are filled with lead glass (crystal). This is also done because up to 70% of the volume of natural ruby can be a variety of voids.
Rubies that have healed pores and cracks with glass look much more presentable from nature-insensitive crystals. It is worth noting that at least 95% of rubies sold at retail are glass-filled.
The consumer is happy to buy bright and clean stones at a price of $ 20 to $ 50 per carat, however, experts complain: the redness of such gems does not produce fiery flashes, is not comparable with the density of blood, and does not glow with hidden fire – but it sparkles with blue and orange. Which is also quite decorative, but … artificial.
A very small part of jewelry rubies (approximately 4%) is created by the thermal diffusion introduction of beryllium. The brightness of the orange-red radiance of these stones is valued above the crystal monolithic shine of glass-filled rubies. Cheaper than a hundred dollars per carat, such stones do not cost under any conditions, and the normal price starts at around 500 dollars per carat.
Unbleached gem-quality rubies are so rare that their value is many times greater than the value of diamonds, and can be calculated in truly astronomical amounts.