Fracture filled

Tiny hairline fractures often pervade the fabric of a gemstone, these can interrupt the flow of light through the stone, thereby creating white or "dead" spots in the overall colour. If these fractures reach the surface of the stone, they can be filled with oil, wax, glass, epoxy, and borax.  Difficult to spot with the naked eye,  these tiny filled cavities can only be viewed under a microscope, so buyers should be aware of this practice. Commonly filled stones are emerald, aquamarine, ruby, sapphire, peridot, and turquoise. Because emeralds are naturally heavily fractured, it is common practice for them to be oiled.

Ruby fractures are filled with a transparent lead glass as the refractive index of corundum and lead glass are very similar which allows light to travel through the stone, improving the colour and clarity. Madagascan rubies disfigured by fissures or surface cracks are often "repaired" using heat treatment with lead glass.  They can be found in large sizes at a fraction of the cost of untreated stones.  These rubies represent an excellent value in the market if the treatment is disclosed and the price is appropriate.

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