By Craig Thomas – FGA(Gem-A), GG(GIA)
Only a small percentage of natural gem quality diamonds are treated. There are two reasons to treat a diamond, 1) To improve or induce colour and 2) To improve the apparent clarity and appearance of the stone.
a) Laser Drilling
A small hole is drilled using a laser to reach the targeted inclusion. The dark inclusion is then vaporized with the laser or bleached to lighten its appearance. Laser drilling is considered a permanent treatment, however dirt can become trapped in the opening increasing its visibility. The drill hole is regarded as a clarity characteristic.
b) Fracture Filling
Is when surface reaching fissures and cavities are filled with a glass like substance to improve the appearance of the stones clarity. This treatment is often used to fill the laser drill holes mentioned above. Fracture filling is not considered a permanent treatment because although the filler can last for years with the proper care, it may be damaged or altered by exposure to heat or chemicals, even ultra sonic cleaners can cause damage to some fracture filled stones.
Fracture filled diamond showing the “flash effect”.
Stones are exposed to various types of radiation to induce yellow, green, brown, blue and black colours. Irradiated diamonds should not be exposed to high temperatures such as during standard jewellery repairs as heat can cause the colour to change.
These blue diamonds were irradiated to induce the greenish blue colour.
Is the controlled heating and cooling of a stone. It can be performed after irradiation to produce brown, orange, yellow, pink, red and purple colours. Annealing can be done without irradiation to change colours in a series, blue to green to brown to yellow. Any further heating of these stones can cause the colour to change dramatically.
This treated yellow diamond was irradiated and then annealed to produce its colour.
High Pressure High Temperature treatment uses a similar process to that used to grow HPHT synthetic diamonds. Brownish stones can become colourless or near colourless, yellow, greenish yellow or green. Some stones may turn pink, blue or orangey yellow. HPHT is considered a permanent treatment.
Colours like pink, red and purple are usually the result of a multi step process that could involve irradiation, annealing and HPHT treatment.
This pinkish purple diamond was treated with a multi-step process.
This ancient treatment can be as simple as blue ink around the girdle of a stone to improve its colour but thanks to advanced technologies thin durable coatings can produce natural looking fancy coloured stones in pinks, oranges, yellows, blues and purples. These coatings are not considered permanent and although they are very durable they may be damaged by heating, chemicals and abrasion.
A very crude form of coating, this stone has blue ink around the girdle in an attempt to improve its apparent colour.
It is clear then that there is a lot that can be done to improve the colour or appearance of a diamond and these treatments all have an effect on the stones value. It is essential to have full disclosure when selling these treated stones as well as advising potential clients of the proper care of treated stones. There is definitely a place for treated diamonds in the market as long as they are not miss represented.
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