Diamonds possess the three attributes that make up a gemstone which are beauty, rarity, and durability. They are also the hardest mineral known. As diamonds were formed deep in the earth billions of years ago, irregularities often developed within. These imperfections may be tiny crystals, referred to as pinpoints, or they may be larger crystals. They may be transparent or dark in appearance. Some diamonds have internal feathers named as such due to their appearance, which can look similar to a feather. When these feathers reach the surface of a diamond they can be treated by a method that uses a glass to fill these fissures. Sometimes this treatment is called clarity enhanced, others may call it glass filled, and some may refer to this process as fracture filled.
The glass filling process has been around for about 30 years. The glass is drawn into the diamond by a vacuum process after it is melted. The feathers are generally so microscopically thin that the glass that goes into the diamond usually will not add any noticeable weight to the diamond however, it can have a dramatic effect on the appearance of the diamond. Feathers that might have been visible to the naked eye are often reduced visibility or not visible at all.
Identification of this glass filling is usually very easy for the jeweler. Due to a property known as refractive index, when light passes through the diamond and the glass filling at the same time, the glass will flash a color-possibly blue, orange, purple, or green. Another identifying feature in a glass filled diamond is the possible presence of tiny gas bubbles. These form as the glass cools from the molten state.
Clarity enhanced diamonds will cost less than a non-treated diamond of similar clarity. The reason is because the diamond clarity grade will improve by one to two grades. The diamond should not sell for the same price as one with equal clarity appearance that has not been treated. Note that Some major laboratories such as the Gemological Institute of America will not offer a grading report on a diamond that has been clarity enhanced.
Special care is needed with the clarity enhanced diamond as the glass filling may not be stable. Repairs that require a jeweler’s torch will definitely damage the glass filling. Likewise, an ultrasonic cleaner may cause the glass to seep out however, in normal daily wear, the glass filling is considered mostly stable. Long-term, the filling can change slightly in appearance if it dries out but a glass filled diamond can usually be retreated if necessary and later years.