The Corundum Conundrum – Part 2

Part 2:

As mentioned in my previous post, Sapphire isn’t just the blue stone that the majority of consumers are familiar with. It occurs in a variety of colours. All these colours coupled with their origins and type, will lend each Sapphire the qualities that define it.

As well as a multitude of colours, Sapphires can exhibit two unique phenomenal occurrences.

Both these phenomena are typical to Sapphire and both will affect value.

One such phenomenon is Colour-Change.

Many colour-change Sapphires come from Sri Lanka and East Africa, particularly Madagascar.

Some in the trade compare them to fine colour-change Alexandrite.

Typically, with strong change, the actual colours are blue and purple.

Colour-change Sapphires will be blue in normal light and purple under incandescent light. Occasionally they may be pink. They will change to a green colour under incandescent light.

Many Sapphires will simply ‘Shift’ colour.

There is a distinct difference. Colour-shift can occur in a Violet stone shifting to Purple. A stone that can ‘change’ from a ‘blueish green’ to a ‘brownish red’ is truly a rare specimen. Colour-change Sapphire will be predominately small in size, and their value differs. Unlike a faceted Gem such as a Padparadsha, clarity and colour take second preference. Here it is the degree of colour-change that is important.

The other phenomenon is Asterism.

It is an optical occurrence visible on the surface of the stone in the form of  star-like Rays. Hence the title: ‘Star Sapphire’.

Star Sapphires have traditionally been very popular, and have been making a comeback. The sharper and straighter the rays and the purer the blue, the more valuable a blue star sapphire.

So how does Asterism occur? You may have heard the term ‘Silks’. If not, don’t worry. ‘Silks’ are fine needle like inclusions found in the stone. They lend that magnificent velvet appearance you see in Blue Sapphires.

In Star Sapphires the resulting Star is due to the reflection of light on parallel arranged inclusions within the stone.

For Star Sapphire, the silks cause a 6, or occasionally a 12 ray Star.

Unlike Faceted Gems, the Star Sapphire is cut in a Cabochon.

When it comes to value, all Sapphires have their own depending factors. Colour is premium when valuing Padparadsha, the degree of colour-change will take precedent when assigning value to a Colour-Change Sapphire.

I’ll explore this in Part 3. As always comments welcome.

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