Like the ruby, sapphires are a form of the mineral corundum. While most commonly used in jewelry, both natural and artificial sapphires are also used in a number of other applications. Manufactured sapphires are often used in decorative crystal boules. Contrary to popular belief, sapphires aren’t just blue. You can find natural sapphires in a variety of colors, including some very rare ones.
Blue sapphires are the most common and popular hue for this gemstone. In natural stones, the blue is often mixed with a secondary color such as green, purple, or violet. When the blue is mixed with purple or violet, it is often thought to be more beautiful and valuable, while green as a secondary color is considered to be less attractive. The same can be said of the gray saturation masks often found in blue sapphires.
Fancy Color Sapphires
While green is considered to be a poor secondary color, when it is found as the primary color in the gemstone these sapphires are considered to be quite valuable and are highly prized for their rarity. The same can be said of yellow, orange, and brown. The very rare colorless sapphires are often used as a substitute for diamonds in many pieces of jewelry.
The most prized and rare color of sapphire however, is pink. Pink sapphires are very rare, particularly when mixed with orange as a secondary color, and they are often priced far more highly than even the highest quality blue gems. This unique color combination is known as padparadscha, and can only found in Vietnam, East Africa, and Sri Lanka. There is no artificial substitute for padparadscha.
Sapphires get their color from impurities that occur within the chromium. For example, when the chromium mixes with vanadium, the resulting sapphire will have varying shades of purple. When traces of iron mix with the chromium, the sapphires will range from pale yellow to green depending on the concentration. It is the mixture of titanium with iron ore inside the chromium that give the most popular sapphires their deep blue color.
Natural sapphires are treated in several ways in order to improve and enhance their color and hue. When heated at temperatures ranging from 500 to 1800 degrees Celsius, the stone loses some inclusions and the color becomes more pure. It is rare to find natural gemstones that have been unheated; these will be sold with a certificate from a gemological laboratory that states there has been no evidence of heat treatment given.
The first synthetic sapphire crystals were developed by French alchemis Auguste Verneuil. His process produces artificial sapphires that are materially identical to natural sapphires, except that they can be created without the flaws that occur in natural stone. Unfortunately, these artificial gemstones have a tendency to break easily.
Today, most artificial sapphires are made using the Czochralski process, which involves dipping a tiny sapphire seed crystal into a crucible made from iridium. The seed crystal is then slowly drawn up at a rate of a single millimeter per hour, crystalizing the alumina in the iridium at the end, creating large strings of crystal. While natural sapphires are used almost exclusively for jewelry and decorative purposes, artificial sapphires have a number of industrial applications as well. In fact, the strength of the crystals produced in this manner make them popular for use in shatter resistant windows, military body armor, and glass.
Artificial sapphire is also gaining popularity for use as an insulator for semiconducting circuits, particularly those in mobile phones, police radios, and satellite communication systems. Artificial sapphire is excellent for these applications because it has a very low conductivity for electricity, while still conducting heat away from internal components quite well.
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