There are two types of procedures that will improve the clarity of a diamond. The first is called laser drilling and the second is called fracture filling (more commonly known as clarity enhancement). Both are considered clarity enhanced diamonds.
All diamonds besides flawless diamonds will have internal characteristics commonly known as inclusions, including black carbon spots, feathers, clouds, bubbles and more.
Laser drilling creates a minute hole in the diamond, allowing for black carbon spots to be cleaned out. This type of enhancement is permanent, which is both an advantage and disadvantage.
On the one hand, the tiny holes, although not visible to the naked eye, will always be in the diamond. On the other hand, the diamond will be clearer for good.
Fracture filling, despite its name, does not mean that the diamond is broken or cracked, rather that the original inclusions are coated with a clear substance to make them invisible to the naked eye.
Diamonds that are filled are cleaned and boiled to remove any dirt and other imperfections, and then they are filled with a microscopic amount of clear material that cloaks the feathers. There are two types of filling used for clarity enhancement.
One using bromide and the other using a silicone based material. The former is the lower quality treatment and can discolor or fade over time. The higher quality treatment can last a lifetime so long as it isn’t exposed to extreme heat (over 1500 degrees) or acid.
Source: Shiree Odiz
Ashcher Cut Clarity Enhanced Diamond Ring With Pave' Diamonds