Below is guiding how to choose best lab made gemstones.
1 - Your colour
Colour is one of the most important aspects of gems, so this often results in the criterion of choosing a gemstone.
Some lab ruby from Burma is described as: "Blood of Paloma", this exceptional red colour is very precise to the eye of the specialist but has nothing to do with the colour of the blood of the animal. In Burma the least wanted colour is called in local dialect: "an Indian in tears" in reference to the fact that the Indians buy all the qualities of gems, but especially the lowest.
And this is the case for all precious stones, colour is paramount and can define certain proveniences: for sapphires: blue Kashmir, blue Burma, london blue topaz and blue Ceylon.
For diamonds, the colours must be frank: white, the purest or else well-differentiated dyes: yellow, pink, red, blue, cognac ...
2 - Its weight and its shape
The weight of loose gems, estimated in carats, conditions its dimensions, and acts exponentially on its price: at the same quality, a 2 carat stone is more expensive than two stones of 1 carat. This rule is verified even more with rare stones.
For the same weight, a precious stone could have been carved in different shapes: shaped like a brilliant, oval, pear, emerald, cushion...
3 - Its purity
The purity that determines transparency in a man made opal is very sought after. The carved stones that do not involve any inclusion see their value strongly increased. In all cases, if there were inclusions, these should not be unsightly (they should not be placed at the base level, the flat part visible when the stone is set).
Either way, inclusions are not always cursed. In some stones, these participate in their aesthetics, so the inclusions in volutes in the sapphires of Kashmir are famous for giving them a softness that together with their colours take them to the rank of being the most beautiful sapphires of the world, the emeralds of Colombia and more especially those of the Muzo mine, they include inclusions known as "the garden of the emerald" that are added to the aesthetics of the stone.
4 - Its cut.
The cut given by the carver to the colour stones or by the diamond smith to the diamonds should be as perfect as possible in order to give the stone its best shine and its fires.
The perfection and the shape of the cut influence the price of the stone. Thus, a mozambique garnet value with a brilliant cut will have, for the same weight, a higher price than a diamond with a fantasy cut.
The facets must be regular in their geometry and well polished, the chamber must be well balanced, neither very important nor very small. The stone should be carved in a good place inside the rough glass so that the colour is well distributed.
For polychromatic stones such as lindy star sapphire, Tanzanite, the cut must be made on the right axes of the glass so that the colour seen by the base is as pleasant as possible.
Source Article : http://buyloosegemstones.over-blog.com/2019/04/know-how-to-choose-your-precious-stone.html