GARNET TOPPED DOUBLET GEMSTONE (GTD)
A doublet is a type of artificial assembled gem composed in two sections. It is often used to imitate other, more expensive gems.
The Garnet Topped Doublet Gemstone (GTD) is a very interesting falsification method in the gem market. Usually, two pieces of material are bonded together, and the materials of the two layers are not necessarily the same! For example, the top layer (called the crown) is garnet, and the lower layer (called the pavilion) is colored glass, hence the name GTD. In another example, some of the the crown is made of sapphire, and the pavilion remain colored glass. This technique is used for gem elements with insufficient color, and the surface with natural features is matched with the bright color of the bottom to make the imitation.
Garnet and glass doublets were first used around 1850 when it was noted that molten glass would adhere to garnet. It was a popular imitation for all types of gems in many colors because the color of the glass became the only color that could be seen. They were still being produced into the early 1900s until actual synthetic gems were introduced.
Soudé gemstone are some composite stones consist of a coloured layer sandwiched between two colourless or pale-coloured pieces of gem material joined at the girdle. The two gem components can be of natural or artificial origin, and may or may not be of the same species as the gem being imitated. These composites are some times referred to as soudé gemstones, and are often used as imitations of faceted emerald and peridot.
These combined stones usually have adhesive marks on the near lumbar edge, and the inconsistent upper and lower gloss also helps us identify. The Suda stone is simpler, and the edge of the waist sometimes has a bond separation (Figure 1-2). If you look at the waist level, you will find the original colorless condition and color interlayer (Figure 3).
In fact, there are more ways to identify these merged stones. Being a professional jeweller allows us to clearly identify the authenticity of a gemstone and prevent clients from encountering an imitation.