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Orange & Blue Sapphires
Orange & Blue Sapphires

Colour Investigation: Sapphire

Throughout history, sapphire has always been associated with the colour blue. This still rings true today, with many consumers unaware of the other coloured varieties available. STACEY LIM reports.

Since ancient times, sapphire has adorned kings, queens and clergy members. A symbol of nobility and truth, it was worn as a talisman to protect from envy and harm. Sapphire comes in many hues, including rare colour-change varieties. Whilst fine velvety Ceylonese blue is unrivalled and attracts a high demand for stones over 1 carat, parti-coloured (when different colours are found in different parts of a structure) and other fancy-coloured sapphires are increasing in popularity as an alternative to diamonds for engagement rings.

The corundum group includes some of the most desired coloured gemstones used for fine jewellery. Corundum is an allochromatic mineral – meaning that it owes its colour to trace impurities. Colourless sapphire, the most chemically pure form of corundum, is rare. Other varieties are coloured by different trace elements in the crystal structure. Atoms of these impurities resonate in light and absorb specific parts of the spectrum. The remaining light reflected to the eye gives colour to the gemstone.

"Parti-coloured and other fancy-coloured sapphires are increasing in popularity as an alternative to diamonds for engagement rings"

Rich blue Ceylonese stones are the most well-known and valuable variety of sapphire. They are the standard against which other blue gems are measured. However, paler versions of this hue are still in high demand. Blue is caused by traces of titanium and iron; the more iron present, the darker the stone.

Green and some yellow sapphires also owe their colour to iron. Chromium influences the red of ruby, and the pinks of pink sapphire. When chromium is paired with iron, it can produce a special orangey pink colour known 33 as padparadscha– a Sinhalese word that translates to ‘lotus flower’. Other sapphire colours include purple-violet, grey, brown and black. A sapphire’s colour is often patchy and uneven, with straight and angular colour banding typically seen in natural stones.

Commonly originating from Australia, parti-coloured stones show a mix of two or three colours: often blue, green and yellow, which can be cut to create a playful flash of colour through the crown facets. Due to their relatively higher availability and affordability, they offer a unique and colourful alternative to blue sapphire.

Rare colour change sapphires exist, with the varying colours dependent on the colouring agents. The more commonly seen stones are from Sri Lanka, and shift from purple under incandescent light to bluish violet in daylight. Natural daylight or fluorescent light contains higher proportions of blue and green wavelengths, causing the gemstone to appear more cool-hued. Incandescent lighting that contains a higher proportion of red wavelengths will cause the gemstone to appear a warmer hue. The intensity of body colour, and the impressiveness of the colour-changing properties greatly influence a stone’s value.

Sapphires are often heat-treated to remove silk inclusions, thus enhancing clarity and richness of colour. Although this treatment does affect the price, it is not adding anything artificial to the stone, so it is an accepted treatment among gemmologists. A stone’s value rests upon the evenness and intensity of colour, the quality of cut, clarity and carat size.

The spectral delights of sapphires continue to capture our hearts.












ABOUT THE AUTHOR
Stacey Lim

Contributor • Registered GAA Gemmologist & Valuer


Stacey Lim FGAA BA Design, is a qualified gemmologist and gemmology teacher/assistant. She is a jewellery designer, marketing manager and passionate communicator on gemmology. For information on gemstones, visit: gem.org.au









Friday, 20 July, 2018 07:11am
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