Besides from diamond, another type of gemstones that is just as equally famous is Corundum. According to Moh's Scale, corundum has a hardness of 9 and a specific gravity ranges from 3.95 to 4.10. Corundum is known for its 2 famous gemstones, namely Ruby and Sapphire.
Color is the main criteria used to distinguish between ruby and sapphire. The colors of ruby include purple, purplish-red, orange-red, and bright red, where bright red ruby commands huge premium and popularity over other types of ruby. For sapphire, there are more varieties in terms of color, and usually derives its name from its color, namely Blue Sapphire, Orange Sapphire, Green Sapphire, Pink Sapphire, Yellow Sapphire, Colorless Sapphire, and Padparadscha (pink-orange).
I believe many of you have heard of unheated and heated gems. The meanings of the two terms are pretty literal, unheated gems are those gems that have not gone through any heating process, whereas heated gems are those gems that have gone through heating process to improve their qualities. So, why do we have to heat those gems? There are various answers to the question, but the two main reasons are as follow:
1. Color Improvement – this does not necessarily mean to only intensify the color of the gems, sapphires from some location, such as Kanchanaburi, are inky blue. Through heating process, we can make the sapphires brighter and less inky. Also, some sapphires may be pale, but once they are heated, they end up with brighter color.
2. Cleanness Improvement – gemstones found in nature usually have inclusions. The plus side of having these inclusions is that it guarantees that the gems are 100% natural. However, since the market has such a high demand for gemstones with high clarity and no inclusions, these inclusions inevitably affect the market price of the gems. Ruby and sapphire generally have various types of inclusions, for example, fracture, fingerprint, needle, silk, and iron stain. Once the gems have gone through the heating process for color improvement purpose, the heat will not only alter the color, but also heal the fractures and dissolve some types of inclusions, including needle, silk, and iron stain.
Improving the quality of gemstones with heating process is a common practice and considered acceptable. The practice is not considered a consumer fraud because the heating technique is a use of heat to improve the gemstone’s quality without adding in any filler or other materials. Supposedly, there are 2 rubies with the same weight and clarity. The first ruby is unheated, but its color is not as good as that of the second ruby, which is heated. In this case, although the first ruby is considered unheated, the second ruby will have a higher market price because the price is primarily determined by the color of the gems, and it is the color that the market values the most when it comes to pricing.