What is "fracture filling" and do I have to worry about it in Gemological Institute of America (GIA)-certified diamonds?

In the mid 1980s, Zvi Yehuda of Israel developed fracture filling to improve a diamond's appearance and to make a sizeable diamond more affordable. The process improves the apparent clarity of a diamond by filling (or concealing) the stone's breaks and laser-drill holes with a glass compound that's poured into fractures using a vacuum and pressure.

The problem with fracture filling is that it's not stable. The filling can be dislodged during simple jewelry repairs, by ultrasonic or steam cleaning, or even by extended exposure to the sun's ultraviolet rays. When the filling falls out, the break in the diamond becomes obvious again.

Although the GIA will not grade a fracture-filled diamond, diamonds are very often fracture filled after they have been certified by the GIA. In addition, fracture filling is very difficult to detect; therefore, many diamond dealers sell fracture-filled diamonds without even knowing themselves that the diamonds were treated.