Cutting and Polishing Gemstones

Some gemstones are used in the form they are found in, and have very little done to them before being sold on. However, most types of gemstones are used in jewellery; so many people want the best possible looking stones. For this, the gemstones need to be cut and polished. Depending on the stone, the cutting and shape will be in one of two categories. The first is when the gemstone is cut and polished into precise angles at fixed intervals, which creates the illusion of many flat windows across the stone. These are called facets. The second category produces a much smoother effect. If the stone is polished into a dome shape, it is called a cabochon. Careful polishing using a grinding wheels and other polishing instruments create the very smooth shape of the dome.

Cabochons are usually created from stones that are opaque, such as turquoise and opal. The shape of the stone really shows off the beauty of the colour.

Transparent gemstones are the types that are faceted. By polishing the surface of the stone into separate fragments, the most inner part of the stone itself will be visible. This type of polishing creates a wonderful light effect and optical illusions. This reflecting and twinkling gives the stone the much desired ‘sparkle’ effect.

The process of faceting is very complex. If the angles are not polished to the exact degree, either too sharp or too shallow, the sparkle effect will not happen at all, and the stone will appear dull with no light reflected from it. And, of course, each gemstone is different, so the angles change depending on the type of stone and the jewellery that will encase it. A special mechanism called a faceting machine is used for this precise process, which holds the gemstone in place.

The Beauty of the Stone’s Colour

The colour of the stone is its selling point, and has a lot to do with the light that surrounds it. If the stone is in daylight (daylight is also called white light, which is a mix of all the colours of light), it will produce the best colour. The stone absorbs some light and allows other kinds to pass through. For example, a ruby appears so deeply red because that is the only colour that passes through it. This all depends on the gemstones chemical composition and atomic arrangement, which changes from stone to stone.

Heating the Gemstone

The clarity or colour of most gemstones can be greatly improved with the addition of heat. It is an age-old process, one that has been taking place in gemology for centuries, and is recognised by gem cutters and miners worldwide. For example, if an amethyst is heated to a certain temperature under specific conditions, it becomes citrine. Most aquamarine gems are heated in order to remove any hints of yellow or green, which enhances its blue to much purer levels. And the same goes for tanzanite. These gems are exposed to low levels of heat, which gets rid of any undertones of brown that occur in the stone naturally, and give a clearer purple appearance to the final result. And nearly all rubies and sapphires are heat treated to boost their clarity and their colour.

Radiation and Gemstones

It’s not just heat that can be applied to gemstones to enhance the final result. Some stones, but radiation too. The deep blue shades of blue topaz are only achieved when the stone is irradiated. Before this occurs, the natural, raw colour of the gem is white. This is also the case with Oro Verde (or greened quartz). The final green-yellow colour is mainly attributed to the irradiation.