RANGE OF HUES

To assess the quality of a Thai ruby, it is important to first determine whether it is red, red-purple, or reddish purple. Generally, gemstones have a certain hue depending on their source, and that hue becomes one of the characteristics of gems from that source. In the case of Thai ruby, color comes in a wide range, from an orangey red to a reddish purple.

Red

A pure red is considered the finest color, with stones of grade 6-S sometimes comparing favorably with the Mogok “pigeon’s blood.” It is difficult to judge whether stones of this type are of Thai or Mogok origin, and it is necessary to collectively consider indications such as inclusions and fluorescence in making a decision. Unfortunately, the color of a large portion of Thai material is too dark, with poor transparency and often a muddy appearance that limits them to jewelry-quality and accessory-quality stones of beauty grades B,C, or D.

Red-Purple (RP)

This is the typical hue for Thai ruby, with many Thai rubies falling onto this category. One of the characteristics of Thai ruby is that even as tone becomes light, hue does not change. This is in contrast to the characteristics of Mogok rubies, which show a more bluish color as they become lighter, changing from red to purple. However, Thai rubies with lighter tones lose their depth of color, resulting in an unfortunate loss of beauty.

Reddish-Purple (rP)

This is a red that is close to purple, with quite a bit of bluish hue visible. However, it is strongly red when compared to the blue-purple of a violet sapphire, falling well within the bounds of red. Attractive stones that would be an S grade within this hue have a beauty grade of B when judged on the scale for rubies.

JUDGING QUALITY

As shown in the preceding discussion of hue ranges, hue is important in judging the quality of Thai rubies. As stones shift towards blue, form red to red-purple to reddish purple, they are judged lower as far as ruby colors are concerned. In the case of reddish purple, even an extremely attractive stone is valued low as a ruby, having a beauty grade of B.

In general, most gemstones are more beautiful when they have a high level of transparency, but occasionally there are Thai rubies that lack depth of color, appearing “watery.” This is attributable to the material itself. When judging quality, ascertain the overall attractiveness through consideration of factors such as the shape and appearance of the stone, uniformity of color, and the presence of inclusions.

The quality scale to the next page consists of rubies chosen from red-purple stones.