Heated or Unheated Sapphire?

An unheated sapphire is naturally suitable for use in jewellery, yet a heated sapphire is not considered "altered". An overview of this age-old technique, its advantages, and why some prefer to avoid it.

What is a heated sapphire?

Heating sapphires is an extremely common process, carried out in a high-temperature kiln (up to approximately 1,800 °C) or by traditional means. It has been practised since Antiquity.

The aim is to improve natural imperfections, inclusions, and any lack of colour intensity or homogeneity. Many blue sapphires are naturally of insufficient quality for use in jewellery, being either too pale or too dark. That said, these precious stones exist in a variety of colours, many of which are heated — the violet sapphire, for instance. The result is notably a richer saturation.

The vast majority of sapphires are heated, regardless of their origin in the world.

What is the price of an unheated sapphire?

In principle, purchasing an unheated blue sapphire costs more than purchasing a heated one. The same holds true for other colours. An unheated sapphire is rarer, and its value increases accordingly. Some stones are even rarer still, such as the unheated Burmese sapphire, renowned for its remarkable purity and brilliance. The same applies to the unheated Ceylon sapphire which, though less rare, is equally prized for its exceptional quality and diversity of hues.

However, the price of a sapphire depends on more than heating alone. The price of a high-quality heated sapphire can very well exceed that of a less exceptional unheated sapphire.

Is it acceptable to heat sapphires?

Whether or not additives are involved (diffusion treatment), heat treatment of sapphire is a wholly accepted practice in the world of fine jewellery. It is noted on gemmological certificates and considered standard — even essential — for a great many stones, including diamonds and the prestigious Burmese rubies. Among precious stones, only the emerald cannot be heated. This process has no bearing on the care of a sapphire ring or any other jewel.

Heated or unheated sapphire: which to choose?

Purchasing an unheated sapphire can offer certain advantages, provided the stone is naturally of good quality, of course. Admirers of authenticity tend to prefer sapphires that have not been enhanced, seeking out rarer stones or collecting those of greater value. For the creation of rings and jewellery, many people turn to heated sapphires because of their price, or simply because they are easier to find, and in a wider variety of shapes and colours. An unheated sapphire ring can require a great deal of searching.

Can a heated sapphire be identified?

A gemmologist has the equipment needed to distinguish a heated sapphire from an unheated one. To the naked eye, it is impossible. That said, take the example of a pink sapphire with brownish undertones: the difference after heating can be seen clearly.

Heat treatment does not alter a sapphire

Heat treatment is not considered a treatment in the strict sense of the term. This is why a heated sapphire is valued no less than an unheated one. Treatments that can significantly alter the nature of a stone are more controversial. But provided they are declared on the certificate of authenticity (as French law requires), there is no deception. A prime example is the treatment known as fracture filling, which involves injecting a substance into the fractures of a stone in order to enhance its appearance and durability. This treatment improves the look of the stone, but it does affect its physical properties.