.....A high percentage of the grading and classification terminology for gems is subjective. For example, there's no general agreement on the exact tonal boundaries of a padparadscha, an orange-pink sapphire. Gem connoisseurs just know that it isn't dark. there's no agreement either on the exact boundaries of an orange-red ruby or a red-orange sapphire and padparadscha is not a good enough reason for us to abandon these terms. Likewise, the lack of a clear dividing line between ruby and pink sapphire is not a valid argument for eliminating the term "pink sapphire" from our vocabulary.

.....The ICA nomenclature is not universally applied. Most of the gem trade in Europe and North America, for example, prefers to treat the pink sapphire as a unique stone with its own merits, rather than as a lower-priced ruby. High-quality pink sapphires are rare and can cost many thousand dollars per carat.

.....Tone is not the only factor used to distinguish ruby from pink sapphire. Hue can also be important. Hot pink, for example, is not light in color;nonetheless it's called pink. The hue of hot pink, however, falls between red and purple, giving it a different look than either of these colors. In the print and photo industries, a red -purple color is called magenta. The general public, however, often calls it "hot pink" or "pink" depending on the depth of color.

.....Once in a while ruby is defined as corundum that's colored mainly by chromium, a metalliec element incorporated into the mineral as an impurity. Dr. Horst Krupp, a mineralogist and dealer, says he determines if a stone is a ruby with the aid of a spectroscope, an instrument which measures how the stone absorbs light. If a reddish corundum stone shows lines in the spectroscope indicating the color is clearly coming from the presence of chromium, then he calls it ruby; otherwise he calls it red sapphire. He was taught to define rubies this way at the University of Heidelberg in Germany.

-Crystals are solid mineral inclusions of various shapes and sizes. Examples of minerals found in corumdum (ruby & sapphire) are pyrite, garnet, zircon, calcite and spinel. Minute crystals are sometimes called pinpoints or grains, and when they are grouped together, they may look like comets, galaxies or falling stars.

-Negative crystals or voids are hollow spaces inside a stone that have the shape of a crystal. They often resemble solid crystals, so for purposes of clarity grading, they're simply called "included crystals."

-Silk in corundum consists of very fine fibers of rutile(titanium dioxide) or other minerals. It can also be made of mineral grains arranged in straight rows. These fibers or rows intersect and resemble silk, hence the name. Well-formed silk can be proof that a stone was not heat treated to improve its color. Very high temperatures tend to dissolve it and make it look fuzzy or dot-like. Since untreated stones are more valued than treated ones, the presence of clear, well-formed silk can be welcome sign.

-Needles are long, thin inclusions that are either solid crystals or tubes filled with gas or liquid, which are called growth tubes.

-Parting (false cleavage), which occurs in corundum, refers to breakage along a plane of weakness. Mineralogist John S. White has determined that parting planes are actually thin seams of another mineral, normally boehmite.

-Twinning can occur when two or more crystals of the same mineral are united with a symmetric relationship. In faceted corundum, twinning usually appears as straight lines, which are in essence flattened twinning planes.

-Halos are circular fractures surrounding a crystal. These structures generally result from stress created by radioactive decay of the crystal inside the halo or from extreme heat. during heat treatment, the included crystal can expand, producing a circular fracture which tends to have a glassy appearance and/or a lacy fringe on the outermost edges of the fracture. the central crystal often melts, sometimes producing a snowball-like core.

-Fingerprints, common in corundum, are thought to be healed cracks. These inclusions often look like human fingerprints, but they may also resemble loopy veils.

-Saturn-like inclusions have a central core with the form of a flattened sphere surrounded by a planar circular, radiating fingerprint. The core can be solid, fluid/gas filled or hollow. The surface of the core may be very smooth and metalic or granular like a snowball, sometimes with a black "pepper-like" appearance. Saturn-like inclusions are often found in THai/Cambodian rubies and are a good example of an inclusion that helps gemologists determine country of origin.

-Growth or color zoning refers to an uneven distribution of color in a stone. If the different color zones look like bands, they are called growth or color bands.

-Cavities are holes or indentations extending into a stone from the surface. Cavities can result when negative crystals or tubes are exposed or when solid crystals are pulled out of a stone during the cutting- process.

-Chips are notches or broken off pieces of stone along the girdle edge or at the culet.