The term "sapphire" refers to a variety of corundum of all shades except red (red corundums are called rubies). However, when talking about sapphire, they usually mean a blue stone. Cut sapphires are gemstones of the highest category; in Russia they are equated to currency values. Determination of the quality of sapphires is made in the following categories: color, clarity, weight and cut quality. These parameters should be indicated on sapphire jewelry tags.
Instructions
Step 1
Color
The color of the sapphire is determined by gemologists visually, when compared with the reference specimens. It is characterized by a combination of hue, saturation and lightness. The main color tone of the stone is pure spectral blue, the acceptable secondary shades are violet and green. Sapphires are also classified into five lightness categories and three color saturation categories. However, for commercial purposes, a simplified color classification of sapphires is usually used, which provides for only three groups. The first is bright blue sapphires; the second - mid-blue sapphires; the third is light blue sapphires.
Step 2
Purity
The clarity of the sapphire is also determined visually, with the naked eye and with a 10x magnifying glass. Four purity groups are accepted. The first one is almost perfectly transparent sapphires without defects or with single small defects, which are noticeable only at significant magnification. The second is transparent stones with few small defects and natural inclusions that are invisible to the naked eye. The third one is sapphires with partial loss of transparency, with defects and inclusions, which are very clearly visible even to the naked eye. Fourth - sapphires with a noticeable or complete loss of transparency, with numerous, well-distinguishable defects and inclusions (or single, but very large defects).
Step 3
Weight
The weight of sapphires is measured in carats (1 carat equals 200 mg). Small stones up to 1-2 carats are quite common. Sapphires from 5 carats are considered large. They are very rare. The cost of 1 carat weight of such a stone, depending on its color and clarity, can reach 4000 dollars.
Step 4
Cut
The main methods of cutting sapphires are faceted and cabochon. Of the faceted cuts, the most common is round, but fancy cuts are also often used: "heart", "emerald", "marquis", "oval" and "pear". A cabochon is a method of cutting in which the stone is given a round or oval shape with a convex polished surface. In this way sapphires are processed with a significant loss of transparency and a large number of defects. The cabochon cut of opaque sapphires with needle-like inclusions of the mineral rutile (the so-called "star" sapphires) reveals the effect of asterism - the appearance of a star with 6 or 12 rays sliding over the surface.
