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Natural or heated sapphire: example of Padparadscha

Heating colored sapphires 

I was disappointed to learn from a trader on my way to Sri Lanka that the most sought-after pink-orange or orange-pink sapphires, called Padparadscha, were heated "most of the time." A light heat treatment performed on site to boost color is therefore common practice to meet the demand of a rapidly growing market for colored stones. These sapphires are heated to a low temperature of 1300 degrees in traditional furnaces and then buried in sand for slow cooling.

This particular color evoking the sunset, is sought for its rarity in the family of corundum that sweeps the entire light spectrum of the visible; by convention the stone of main red hue is called ruby, the blue, sapphire, and for all other colors, we specify the dominant color and then secondary possibly (colorless sapphire, yellow-orange, pink, green ...).

Exception for Padparadscha (meaning lotus flower) which marries the two shades, with a dominant orange or pink, whose trade name comes from the story of the Tamil people beautifully told in Jacques David's latest novel "Padparadscha", published in 2017 by Jets d'encre.

Natural or treated stone?

The Decree n°2002-65 of January 14, 2002 relating to the trade of gemstones and pearls in France has clearly distinguished between "traditional lapidary practices" such as "heat treatment, provided that any residues of heating on the surface do not cause a break in the reflection visible with a 10x magnification magnifying glass".

While on the other hand, stones that have undergone "treatment by irradiation, laser, dye, surface diffusion, filling, possibly as a residue of heat treatment, colorless foreign matter solidified in the outer cavities that show breaks in reflection visible with a magnifying glass of 10 times magnification, or any other laboratory method that modifies their appearance, color or purity" must be marked "treated".

Not easy to distinguish between the two! Depending on the temperature, heating is considered in some cases as a "traditional" heat treatment and in other cases, it can modify the color and/or inclusions contained in the "treated" stone.

Clearly, either the stone is natural, without heating, or it has undergone a light "traditional" heating, or it has been treated by heating to 1600 ° combined with other chemical elements in order to modify the color and make it pure.

The price

Considering that the price differences are significant for natural, unheated and untreated stones, reaching up to 13,000 €/carat in the case of Padparadscha, the question of the heating technique is important to know.

Synthetic stone or imitation?

Participating in a think tank with other non-gem experts, I realized the possible confusion between the two cases.

Above all, it is essential to know the name of the mineral species which is sometimes different from its commercial designation: the term "water sapphire" used in the field of lithotherapy seems inappropriate to me; it is actually a species called cordierite or iolite which presents an optical phenomenon called trichroism (3 distinct colors visible according to the orientation of the stone in relation to its optical axis) and which has nothing to do with sapphire (family of corundum) which only presents a pleochroism (2 colors).

Synthetic sapphires: several processes

Then, on the jewelry market, synthetic sapphires abound that have undergone, in addition, a treatment on their color or purity to blur any identification of the methods used.

These synthetic sapphires are therefore stones produced in a laboratory from the same chemical elements; certain characteristic inclusions are visible with a magnifying glass (Verneuil process developed at the end of the 19th century) which can be a source of confusion when selling because it is indeed a "sapphire" to which we must add "synthetic" according to French legislation; man has produced a sapphire with the same main characteristics of the stone: its hardness, density, for example, but in the laboratory.

In the end, very little difference to the naked eye you might say.

The case of an imitation stone

On the other hand, imitation stones are natural stones or stones treated in order to confuse them with the original ... you still follow me? For example, we could mount a red glass emerald cut stone set with diamonds, sold as imitating a ruby. Glass is not a synthetic stone, it is another material that imitates the color of ruby.

Conclusion

Color remains a primary factor in the calculation of price, but it is not the exclusive criterion; the quality of the cut with the respect of proportions, in particular between the base, the table, the facets, the purity, the zones of color, the polishing, all these criteria enter in consideration for rare gems.

From my point of view, the natural inclusions characteristic of corundum, visible with a magnifying glass, remain the best evidence of the traces of the natural growth of crystallization and are source of proof sometimes of the origin of the deposit. Burma, Sri Lanka are the most sought after origins, other deposits, Australia and Madagascar produce beautiful colored sapphires.

The appreciation of color shades may vary from region to region according to cultural tastes and symbolic aspects.

To appreciate, let's learn to look at the details with a magnifying glass!