Gem Enhancements Our November Meeting

November 2016 Meeting:  David Bellamy – Gem Enhancements by Liz Kennedy David Bellamy treated the members to a very interesting and informative talk on gem enhancements. David made it very […]

November 2016 Meeting:  David Bellamy – Gem Enhancements by Liz Kennedy

David Bellamy treated the members to a very interesting and informative talk on gem enhancements. David made it very clear that lapidary work does not count as gem enhancement as it does not change the colour, clarity or structure of the piece. Enhancements are done to improve the quality of the gemstone. The three major ways to enhance gemstones are by: Heat Treating, Radiation and Other Additions. Any treatment of the stone should be disclosed and the buyer charged accordingly.

Heat Treatment
Sapphires are almost always heat treated. They are heated to 1600°C in a reducing (no oxygen) environment. a1A1Sapphire crystals often have rutile needles which make the stones cloudy. Heating the sapphire to near the melting point of the titanium causes the titanium to leave the rutile crystals clearing the stone and leaving the sapphire with a much better colour. Keep in mind that sapphires come in all colours.
You can also get diffusion treated sapphires where the faceted stone is tumbled with iron and titanium oxides and then recut. Unfortunately this is only a surface colour and if it needs to be repolished in the future the coating may be removed changing the colour and look of the stone. Beryllium can also be used with sapphires making them orange or yellow.
Tanzanite  is also often heat treated. When heated in an oxygen environment they turn orange. In a reducing environment they go purple. Topaz when heated goes pink. Tiger Eye when heat treated goes from the normal brown to red. It is possible to do this in your own oven at home.

Aquamarines are often a washed out pale blue colour. Heat treatment gives the more popular sky blue colour. a2
Another popular stone that is heat treated is Amethyst. When heated it goes yellow/orange making it citrine. If overheated it gets really orange. Lemon quartz is made by heat treating amethyst until it goes lemony yellow.
Prasiolite from certain areas of the world will form green amethyst when heated. There is some discussion as to whether Ametrine is real (made by nature) or man-made. If amethyst is heated it goes to citrine and them the parts you want to remain orange are covered with foil and then the whole piece is irradiated and the exposed areas turn purple.
High Pressure High Temperature (HPTP) treatment of diamonds can turn a cloudy poorly coloured diamond clear.

Radiation Treatment
Many stones are treated with radiation to enhance colour and clarity. Quartz can be irradiated to form smoky quartz. Amazonite when irradiated turns a beautiful green colour. Pure topaz is clear and colourless but is often found yellow or a very pale blue. When the pale blue is irradiated it goes dark blue. The colour topaz goes depends on the type of radiation used and the impurities present in the stone you are using. Diamonds can be irradiated to get different colours.

Other Additions to Stones
From fragile stones like opal and ammolite, doublets (a wafer of opal is placed on backing using black cement) and triplets (a quartz cap is glued on a doublet using clear cement) can be made. These enhance the colour and protect the material. They are less expensive than a solid opal or ammonite.
Black opals have been enhanced by the sugar treatment. The opal is left to sit in a sugar solution for days then it is removed and treated with sulphuric acid. This turns the sugar black (solid carbon) and this really enhances the colour of the stone.
Agates which have very small pores can be enhanced by the sugar treatment to turn them dark brown. Natural agates can also be dyed to produce the variety of colours we see today. They use potassium ferrocyanide to make a3them blue.
Most turquoise is too soft to use so it is stabilized with resin. The resin makes it look wet so it darkens the colour.
Howlite which is naturally white and grey is dyed blue to look like turquoise. It can also be dyed many different colours.
Emeralds can be oil treated. The emerald is placed in a vacuum chamber. This sucks the oil into the stone filling the cracks making poorer quality emeralds look much better. Rubies are filled with molten leaded red glass. You will see orange and blue flashes when turning them.
Diamonds, topaz and quartz can have metal coatings put on them by vapour deposition producing some beautiful iridescent crystals and stones. Examples of this are mystic topaz, aqua aura quartz (gold), rainbow aura quartz (platinum), red aura (pallidium) and aurora quartz (titanium).a4
Tanzanite and sapphire can be ink treated, where the pavilion of the stone is treated with ink to enhance the colour.
Bleaching of pearls with peroxide removes brown and other unwanted colours. Jadeite is bleached and treated with resin afterward. Coral is bleached until the unsightly colour is gone then they are dyed the desired colour.
Diamonds can be laser drilled down to the inclusion then the hole is filled with a material with the same index of refraction of the diamond. Diamond is the only material which can withstand this treatment so it is not used on other stones.

We would like to thank David for an excellent presentation.   All pictures are by Chris  Robart.