Fracture filling, also known as glass infilling, is a process of improving diamond clarity and transparency by filling cracks with a substance that makes the cracks almost invisible.

A diamond that looks like it cost $2,000 for example may sell for only $1,500. Unfortunately, not all jewelers may inform the buyer that the diamond is fracture-filled and the process isn't always permanent. Long-term exposure to cleaning agents, sunlight, or heating may cause the filler to discolor or partially dissolve.

A 10X loupe can be used to detect some, but not all fillings. A binocular microscope with good lighting may be needed to detect some fillings. Ways to detect fracture filled diamonds include looking for:

Color flashes. Fracture filled diamonds show flashes of color in the filled areas as the diamonds are rotated. These flashes show the outline of the fracture or laser drill hole.

Cloudy areas. Filled diamonds can show white cloudy areas or groups of tiny bubbles.

Bubbles. Fracture-filled diamonds may show trapped bubbles, which can be very tiny to quite large.

Some names for fracture-treated diamonds include Yehuda treated diamonds, Koss-treated diamonds, and Goldman Oved treated diamonds.