Diamonds are commonly treated by color- and/or clarity-enhancement processes to improve their appearance and their chance to be sold.
Some of these processes are permanent while others can be removed. In both cases, the enhanced diamond must be properly disclosed before a client.

Clarity enhancements:

Fracture Filling:
Fracture filling is a process for filling surface-reaching fractures in diamonds. Its purpose is to improve the clarity of the diamond by optically hiding the fracture. The fracture is filled with a filler possessing optical qualities close to those of a diamond. Most of these fillers are non-permanent and can be extracted using strong acids and/or heating.
The treatment can be identified under magnification.

Fracture filled diamond. The filled fracture can be identified by its colorful flash effect.

Laser drilling:
The laser drilling process is often used to remove dark inclusions and improve a diamond’s clarity. A tiny laser beam is used to drill into the diamond to create a permanent path from the noticeable inclusion to outside of the gem.
The inclusions are then dissolved by corrosive acids that bleach the dark inclusions, but don’t harm the diamond itself.
The treatment can be identified under magnification.

Laser drilling in a diamond. The entrance points are marked in black.

K.M. Laser treatment:
The KM process ("Kiduah Meyuhad" – special drill in Hebrew) is a newer type of laser enhancement, which creates subtle cracks from the inclusion towards the diamond’s surface. This caused the prominent tunnel to be masked by a series of cracks.
The imperfection is then removed, and the remaining marks appear more like natural flaws than laser trails.
The treatment can be identified by experienced gemologist under magnification.
 

KM laser treated diamond

Color enhancements:

High Pressure High Temperature (HPHT):
HPHT, also abbreviated as HP or HTHP, is a process that converts tinted diamonds to colorless/near colorless range (D to G) and/or yield intense fancy colors. The treatment involves subjecting the diamond into a chamber with high pressure and high temperature. Occasionally, diamonds are treated by multi-step process, which includes HPHT, to produce certain colors.
The treatment can be identified only by using advanced instrumentation.

A ring set with HPHT-treated red diamonds

Irradiation:
Irradiation of diamonds, using a nuclear reactor or linear accelerator, sometimes combined with heating, is used to produce a variety of different fancy colors.
The treatment can be identified only by using advanced instrumentation.

Irradiated diamond

Coating:
Coating of diamonds, using few-micron thick layer, is used to produce a variety of different colors.
The treatment can be identified only by experienced gemologist under magnification and by using advanced instrumentation.


Most gemological laboratories limit their gemological reports to enhanced diamonds with permanent treatments only. GWLAB on the other hand, recognizes the importance of these gems in the trade and provides gemological reports for all types of treatments, distinctly stating the existence of the treatment and its stability.