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Articles from GEMSTONES - LOOSE (254 Articles)

The gem detective: red gemstones

Faceted, red gemstones represent the colour of love, fire and passion, and are always in demand. What could they be? MEGAN AUSTIN reports.

You don’t have to be a super-sleuth to identify the most popular suspect on the red list: ruby, the gemstone of love from the corundum family. From vibrant red to purplish red, rubies boast stunning colours combined with strong fluorescence and tiny inclusions of rutile silk that produce a velvety softness and warm glow irresistible to many.

A ruby’s origin is not necessarily indicative of quality, and rubies of great beauty are mined in Burma, Madagascar, Tanzania and Mozambique. The high value of ruby makes it an attractive target for treatments, synthetics and imitations. Traditional heat treatments improve colour and clarity, while a common variation of this is flux-assisted healing of fissures where surface-reaching fractures are filled with a borax-type additive during the heating process.

Other treatments can significantly alter the appearance and value of a ruby – lead glass-filling turns inexpensive low-grade corundum into bright red rubies, yet these gemstones are unstable as the glass filling deteriorates with exposure to weak acids like lemon juice.

Beryllium Surface or Sub-Surface Lattice Diffusion treatment transforms low-quality, off-coloured corundum into beautiful, vibrant red using high-temperature heat treatment in combination with beryllium.

Synthetic ruby is relatively easy to identify, especially if grown by the Verneuil or Czochralski techniques; however, synthetic flux-grown rubies have a more natural appearance and can be difficult to separate.

Watch for ‘composites’ that are intended to imitate ruby. Garnet-topped doublets, used in antique jewellery, are composed of a hard almandine garnet top fused to a red glass pavilion, while ruby doublets have a natural corundum top and a red glass or synthetic ruby pavilion.

Another ruby imitation is quench-crackled quartz – colourless quartz is heated and then quenched in a cold liquid solution that contains a red dye. This quenching method is also used on synthetic ruby to give it natural-looking inclusions.

Red spinel, previously known as ‘poor man’s ruby’, is capable of achieving the pure, vivid saturations of ruby without the hefty price tag. Synthetic red spinel is extremely rare.

Besides spinel, two gemstones that consumers frequently confuse with ruby are garnet and tourmaline. Red garnet varieties include orange-red almandine, purplish-red rhodolite and deep-red pyrope. Red tourmaline, known as rubellite, may have a purple, orange or brown secondary tint and displays doubling of the back facets when examined with a loupe, as does zircon.

Next up is red diamond, a rare beauty that is usually reserved for wealthy collectors but a cheaper alternative is available in the form of synthetic or high pressure high temperature (HPHT) treated diamond. A simple imitation of red diamond is achieved by applying a red film to the pavilion facets of a white diamond.

Red is a challenging colour category. Some uncommon natural red gemstones are sphalerite, sphene and fire opal, while synthetic and man-made imitators include glass and cubic zirconia.

When in doubt, trust a local gemmologist or registered NCJV valuer to separate and identify unknown red gemstones.

Megan Austin

Megan Austin FGAA FGA Dip DT BA, is a gemmologist and registered valuer. She operates Megan Austin Valuations.

Australian Diamond Trading Corporation (ADTC)

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