Ruby grading standards are mainly based on 1T and 4C: Transparency, Colour, Clarity, Cut, Carat weight.
1. Transparency: refers to the extent to which a gemstone allows visible light to pass through.
In the naked eye identification of rubies, the transparency is generally divided into five levels: transparent, translucent, translucent, sub-transparent, and opaque.
Transparent
It allows most of the light to pass through, and when you look at the objects behind it through the gemstone, you can see clear outlines and details.
2. Sub-transparent
It can allow more light to pass through. When observing the object behind it through the gemstone, the outline of the object can be seen, but the details are blurred.
3. Translucent
It can allow part of the light to pass through. When observing the object behind it through the gemstone, only the outline shadow of the object can be seen, and the details are not visible.
4. Sub-transparent
Only a small amount of light can pass through the edges of the gemstones, but the objects behind them cannot be seen through the gemstones.
5. Opaque
Basically, light is not allowed to pass through, and light is totally absorbed or reflected by the object.
Second, color: refers to the color of the gemstone under natural light.
Color: refers to the color of the gemstone under natural light. Since the light source has a great influence on the color of the red sapphire, the method for observing the classification of the red sapphire is clearly as follows:
1. Place the gemstone under a white background;
2. Observe from the gem table;
3. Observe the ruby ​​under natural light. Usually the more pure and rich the ruby ​​color, the higher the quality and the higher the value. After combining various factors affecting the color of red sapphire, we divided the red sapphire into five levels, including ruby, red, medium red, light red, and light red. Consumers can simply grade the ruby ​​color by simply comparing the five levels of ruby. When grading colors, it is necessary to consider the effect of uniformity of color distribution and anti-fire (internal reflection light caused by cutting) on ​​the grading of ruby ​​color. Usually, they can raise or decrease the color level of red sapphire by one sub-level.
3. Clarity: refers to the amount of inclusions contained in the gem.
Clarity: refers to the amount of inclusions contained in the gem. Red sapphire usually contains a certain amount of inclusions. The size, quantity, vividness and position of the inclusions have an important influence on the value of red sapphire. Under the naked eye, the level of red sapphire is divided into five levels, see the red sapphire clarity scale.
Red sapphire clarity scale
Level clarity observation
It is extremely difficult to see the first level. It is extremely difficult to see the inside of the gem. It is only occasionally visible that the fine needle-like minerals are generally difficult to see in the pavilion.
It is difficult for the second level to see the inside of the gem. It is difficult to see the inside of the gem. The other minerals that are generally colorless or similar in color to the gemstone are generally difficult to see on the edge of the countertop or difficult to see in the pavilion.
At the third level, the internal contents of the gemstone can be seen under the naked eye. Generally, the larger colorless or other minerals similar in color to the gemstone are generally difficult to see at the edge of the table or visible at the pavilion.
The fourth grade is easy to see under the naked eye. It is easy to see the internal contents of the gemstone. Generally, it is a small crack or other mineral with different color and gemstone. It is generally visible on the countertop or in a pavilion.
The fifth grade is very easy to see under the naked eye. It is easy to see the internal contents of the gemstone. Generally, large cracks or larger minerals appear in various positions inside the gemstone.
Fourth, cut: including the orientation, type, proportion, symmetry, polishing degree of cutting.
Cut: including the orientation, type, proportion, symmetry, and degree of polishing of the cutting. Orientation of red sapphire mineral crystals: red sapphire minerals
The crystals are generally in the form of barrels, columns and plates, as shown in the above figure. The vertical direction of the mineral crystal of red sapphire is called the C axis. It is assumed that a faceted gemstone can be cut into facet X and facet Z, where the table top of X is perpendicular to the C axis, and the table top of Z is parallel to the C axis. From the image on the right, we can see the difference between facet X and facet Z: facet Z obviously has dichroism. Therefore, we should try to make the stone surface of the gemstone perpendicular to the C axis when cutting the rough stone, because the value of the gemstone without dichroism is significantly higher than that of the gemstone with dichroism.
Type of cut: Red sapphire cuts include faceted gemstones and plain gemstones, the basic shape of which is shown below. Larger particles of red sapphire are generally mixed cut. Usually, the crown is cut with a bright shape, which makes the gem show a fascinating anti-fire. The pavilion adopts a trapezoidal cut, which makes the gem take care and gains more. Good color.
The proportion and symmetry of the cut: the color of the red sapphire is the embodiment of its value. In order to achieve bright colors, the cutting angle of the red sapphire does not have a qualitative statement, but the following questions will indeed cut the proportion of red sapphire cut. And symmetry cause no small negative effects: very obvious asymmetry: Although the asymmetry of red sapphire is inevitable, the obvious asymmetry will seriously affect the light of red sapphire.
Bottom eccentricity: Severe deviation of the facet from the center will affect the uniform reflection of light from the pavilion, and will also adversely affect the anti-fire of red sapphire.
The pavilion is too deep: some lighter faceted red sapphire pavilions are usually cut deeper to deepen the color of the gemstone, which is understandable. However, some darker gems adopt this cutting method in order to take care of themselves, but have a greater impact on the color, and in most cases the price of the gems is calculated by multiplying the weight by the unit price per carat. Therefore, when considering the price of precious stones, you should also consider their pavilion depth.
The pavilion is too thin: too thin pavilion will make the light enter the gemstone and cannot be reflected out, thus forming a larger window area, which is also known as "light leakage", which will also have a greater value for red sapphire. Impact.
Polishing degree: The degree of polishing affects the luster and anti-fire of red sapphire, so it is also an indispensable factor in the evaluation of cutting.
5. Carat weight: refers to the weight of the stone.
Carat weight: refers to the weight of the gemstone red sapphire under the same quality conditions, the greater the weight, the higher the price, especially the price of high quality red sapphire above 1 carat is more geometrical increments. The size and weight correspondence table of the common red sapphire facets lists the correspondence between the size and weight of the common red sapphire facets.
Ruby weight estimation formula
Circular diameter 2 × height × 4.00 × 0.0018
Oval diameter 2 × height × 4.00 × 0.0020 (diameter: length, width average)
Square hybrid shape diameter 2 × height × 4.00 × 0.0018 (diameter: vertical, horizontal and diagonal average)
Long mixed shape average width 2 × height × 4.00 × 0.0022 (diameter: length, width average)
Square emerald shape diameter 2 × height × 4.00 × 0.0023
Rectangular emerald shape diameter 2 × height × 4.00 × 0.0025
Square average width 2 × height × 4.00 × 0.0024
Droplet shape diameter 2 × height × 4.00 × 0.0018
Horse eye diameter 2 × height × 4.00 × 0.0017
Heart shape diameter 2 × height × 4.00 × 0.0021
Note: The above formula is based on the medium thickness of the waist, the pavilion is not prominent, and the symmetry is better. A thicker waist may require a correction of up to 10% (corrected weight = original weight + original weight x 10%), a prominent pavilion may require an 18% correction, and an asymmetrical shape may require a 10% correction.
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