Filling

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Filling is a gemstone enhancement method which indicates a broad range of treatments. From simple oiling to resin impregnation to the filling of fractures with glass or synthetic gem material with the aid of fluxes.

Oiling

Oiling has been around since antiquity and is still one of the most commonly encountered gemstone treatments. It incorporates the filling of surface reaching fractures in both rough and cut stones with the aid of an oil. Applying oil, with a refractive index near that of the stone it's being applied to, hides the cracks in the gemstone and gives the stone the appearance of more color. Care should be taken when handling such treated gemstones as the oil can easily be removed by detergents or an organic solvent such as benzene. This treatment is not stable; the oil will dry out over time.

Impregnation

Resin impregnation is a relatively new technique which probably saw the light of day in the 1990's. Instead of oil an epoxy resin is used to fill the cracks. Resins are not just used to fill surface reaching fractures but also to stabilize and color porous materials such as opals, jade and turquoise.

Glass filling

Diamonds

Filled diamond.png
According to their own website, Yehuda has been glass filling diamonds since 1982. The first reports of this treatment came in 1987 though when Koivula published an article on it in the G&G. The characteristic ‘flash-effect’ gives this treatment away, note the iridecent colors in the top right corner of this filled diamond on the right. Flow structures indicate the presence of glass as well.

Rubies

Surface reaching cracks in rubies have been filled with lead glass from at least 1984. In this year the first filled stones were submitted to labs. This was colorless glass that had been used to fill surface cavities. The presence of gas bubbles in the glass filler proved an easy method to spot these fillings together with the difference of lustre of the filled areas versus the rest of the stone.

Glass filled ruby.png
Glass filled ruby2.png



These days we see a lot of lead glass filled rubies which are produced from Mozambican low quality starting material. The filled areas can be spotted by the ‘blue flash’, the occaisional bubble and lustre difference. The glass used is susceptible to chemical wear when brought in contact with acids. Even lemon juice and vinegar will damage the glass after relatively short contact periods as you can clearly see in the image below:

Glass filled ruby after acid attack.png


Flux filling

In 1992 a new filling method presented gemologists with another challenge: the flux healing of sapphires. The new ruby find in Myanmar at Mong Hsu produced a lot of fractured crystals. Thai burners enhanced the unattractive appearance of these stones by first cleaning them with acids and then heating them in a flux with or without AlO2. This causes a ‘synthetic’ intergrowth of corundum to occur in the cracks which seals them. A very nifty treatment which aids the gemstone a lot, both in appearance and in durability. There are no known issues with this treatment in terms of durability.

They may serve as a good clue to the appraiser though. The flux healing almost always leaves flux feathers in the used-to-be cracks. The course nature and opaqueness of these flux remnants act as a readily identifyable feature which dates rubies to post 1992.

Table

Material Effect Date of introduction
Filling
Beryl (Emerald) Clarity/color enhancement by (colored) oil or epoxy resin Oil – BC


Epoxy resin – 1994 ( Levy, 1994 ICA gazette, april)

Corundum Clarity/color enhancement


Oiling

Glass filling





Flux healing




BC


BC

Glass filling of surface reaching cavities in rubies 1984 (http://www.ruby-sapphire.com/foreign-affairs.htm Hughes, 1992]

Flux healing of surface reaching cavities in rubies 1992 (http://www.ruby-sapphire.com/foreign-affairs.htm Hughes, 1992)

Diamond Glass filling 1982, Zvi Yehuda
Jade color/stability enhancement:


Impregnation
B-jade
C-jade

?

? ?

Opal Impregnation:

stability enhancement

?
Turquoise Impregnation:

color and stability enhancement

?
Lang Antiques
Lang Antiques