Ruby: The Exquisite July Birthstone

Origins and Value

Grading and Evaluation Standards

1. Transparency: This refers to the degree to which a ruby allows visible light to pass through. In visual appraisal, transparency is classified into five levels: transparent, sub-transparent, translucent, sub-translucent, and opaque. Transparent rubies are the most visually appealing and, consequently, the most valuable. A slight increase in transparency can lead to a substantial increase in price, with each successive level typically commanding a significantly higher price than the previous one.
2. Color: The specific shade and intensity of the red color are critical. The ideal ruby color is pure and saturated, without any traces of off-color or other hues. The most sought-after color is "Pigeon Blood Red," which exhibits a deep, intense red that resembles the color of blood and conveys a sense of "burning flame."
3. Clarity: Rubies are known to have a relatively high number of impurities, including cracks, flaws, and fissures. However, the presence of these inclusions does not necessarily detract from the ruby's value. In fact, they can sometimes add to the stone's character and authenticity. The key is the location and visual impact of these inclusions. If they are not overly prominent or do not significantly affect the overall appearance of the ruby, they may be considered acceptable.
4. Cut: The cut of a ruby is a delicate art. Unlike diamonds, where the goal is often to maximize brilliance through geometric precision, the cut of a ruby aims to enhance and preserve the natural beauty of the stone. For darker rubies, a shallower cut may be preferred to allow more light to penetrate and bring out the color. In contrast, a deeper cut may be more suitable for lighter rubies to intensify the color. A well-cut ruby will evenly distribute and reflect light across its surface, creating a lively and dynamic play of colors.
5. Carat Weight: As with most gemstones, larger rubies generally command higher prices. However, the quality of the other factors, such as color, clarity, and cut, must also be taken into account. Rubies weighing 3 carats or more are considered rare and highly valuable, and those exceeding 5 carats are extremely scarce.

Identification Steps

1. Distinguishing from Substitutes: When identifying rubies, it is essential to differentiate them from similar red gemstones. Red spinel, for example, has a uniform color and lacks dichroism, which is a key characteristic of rubies. Pyrope garnet also exhibits a uniform color and no dichroism. Red tourmaline may contain gas-liquid inclusions and display double images on facet cuts. Red glass, on the other hand, has gas inclusions, a lower density, a glassy luster, and feels lighter in the hand. Synthetic rubies pose a particular challenge as they can closely resemble natural rubies in terms of specific gravity, hardness, and color. However, they often lack the natural imperfections and inclusions of genuine rubies, appearing overly perfect, with an unnaturally uniform color, strong fluorescence, and sometimes larger particle sizes.
2. Analyzing the Origin: Different ruby-producing regions yield stones with distinct characteristics. Myanmar rubies, as mentioned earlier, are known for their vivid colors, including pigeon blood red and rose red. The color is often uneven, with a distinct pleochroism that resembles red syrup. They commonly exhibit the asterism effect and contain various solid inclusions such as spinel, calcite, zircon, and hematite, which are typically rounded in shape. Thai rubies have a brownish-red tone, with straight color bands and growth lines and fewer inclusions. Sri Lankan rubies are lighter in color, have fewer inclusions, and possess good transparency. Vietnamese rubies are characterized by light pink, pink, and rose red colors and may have cloud-like inclusions. Rubies from Yunnan, China, are red and rose red and contain gas-liquid inclusions. Identifying the origin of a ruby can provide valuable insights into its quality and value, as prices can vary significantly depending on the source.
3. Determining Heat Treatment: The majority of rubies on the market today have undergone heat treatment. This process can enhance the color, increase transparency, and eliminate certain internal flaws such as color bands and some inclusions. It can also heal fractures, thereby improving the overall appearance of the ruby. However, it is important to note that heat-treated rubies are not considered fake but rather enhanced. Diffusion-treated rubies, which involve the introduction of chromium into the lattice of colorless corundum to produce a red color, have a distinct color distribution pattern. The color appears in an irregular spider-web-like, net-like, or striped pattern, with deeper coloration at the corners and fractures and lighter color elsewhere. Reagent-dyed rubies, on the other hand, are created by heating colorless or light-colored corundum with fractures and then immersing it in a dyeing agent. These rubies have an unnatural color that is darker and may have a yellowish tint. Under long ultraviolet light, they do not exhibit the characteristic red fluorescence of natural rubies but instead show yellow fluorescence at the fracture sites. Their absorption spectrum is also weaker than that of natural rubies, especially in the red region.
4. Checking for Fillers: Some rubies may have been treated with fillers such as oil, paraffin, plastic, or glass. These fillers are injected into the fractures, holes, or pores of the ruby to improve its appearance. When examining a ruby for fillers, one should look for signs such as flow marks and bubbles in the interstitial materials under a microscope. The presence of bubbles is a clear indication of artificial filling. Rubies with fillers may also exhibit a rainbow effect along the filling seams, and there may be a difference in luster between the ruby and the filler. Under reflected light magnification, an interference effect can be observed. If a thermal conductivity meter is used, oil beads may be sucked out when the needle is placed near the fracture. Under a polarizing microscope, the homogeneous filler may show a total extinction phenomenon. Under long ultraviolet light, the filler at the fracture emits a dull yellow fluorescence, while the ruby emits red fluorescence. If the filler is a high-molecular organic compound, it will have a strong absorption effect on infrared rays. After ultrasonic cleaning or heating, white deposits may be visible in the fractures. Additionally, filled rubies may have an oily appearance that can sometimes be detected by the naked eye.