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Gemstones that look dull or have a matte finish have not been polished. Most gemstones in their natural state look rather dull and unimpressive. It is only by polishing that the gems are able to take on that glass like sheen we see in the jewellry store. Polishing takes place by using abrasive materials that become finer and finer as the polishing progresses.
Polishing
Before a polished gemstone emerges the rough rock must be cut into the desired shape. The cutting is usually done using a diamond-banded saw. As diamond is the hardest material on earth it will cut through all gemstones including itself. Cutting a gemstone must be done slowly and carefully to prevent splitting the jewel. The cut stone is then sanded to get rid of any obvious harsh marks and gouges. Finally using coarse grit, the gem is polished to resemble a brilliant mirror reflecting or refracting light to give it that bright sparkle.
Polishing Agents
While fine diamond grit or dust can be used to polish rough gemstone other materials are also used depending on the hardness of the stone being polished. Metal oxides are a popular alternative and include aluminum oxide, cerium oxide, ferric oxide also known as jeweler’s rouge and silicon dioxide to name a few.
The shape of the stone as well as the type of stone can also determine what polish is used. For a flat surface tin, leather, wood or felt can be used. On a round surface a polished gemstone needs cork, cloth, or wood to get that glass-like appearance.
It is up to the lapidary (professional polisher) to determine what type of polish should be used for what type of gemstone. A wrong guess could ruin a stone that might have been worth thousands of dollars. Needless to say polished gemstones are true works of art that have taken careful planning and execution to complete.
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