Sapphires have long been prized for their vibrant deep blue color. There has been mystique surrounding these gems ever since Prince Charles gave Diana Spencer an engagement ring featuring this brilliant stone.
Sapphires are mined around the world, in countries as far-flung as Thailand, Eastern Australia, East Africa and the United States (Montana). Those born in the month of September wear sapphire as their birthstone and it is also used to celebrate a 45th wedding anniversary because it's a stone that symbolizes faithfulness. The largest faceted blue sapphire known to exist is housed at the National Museum of Natural History in Washington, DC: the 422.99 carat Logan Sapphire.
There are several criteria by which to judge high-quality sapphires, the most important of which is color. The most sought-after stones feature a deep royal blue color which does not fade or change when looked at in different levels of light.
It's also important that the surface of the gem be unblemished with no inclusions (small foreign bodies) that are visible to the naked eye. You should also be able to verify whether the sapphire has been treated with irradiation, heat, dye, or any other chemical coating process which may lower the value of the stone.
The cut of the sapphire can make one sapphire more valuable than another. Sapphires that exhibit flaws on the stone's surface, irregular shapes, and poor polish or symmetry make an inferior investment. Oval shapes have been perhaps the most popular cut for sapphires since Princess Diana's famous ring, but you should not automatically opt for this cut as each sapphire is best cut to optimize its color and brilliance. Check to see that the edges of the stone you are considering are symmetrical and even. The top of the gem, called the "crown", should also be even in size and shape and well-centered. The most high-quality stones will flash brilliant displays of color no matter in what direction the stone is tilted. Take a pass on any stone that has uneven color or does not reflect light evenly from every angle, as these are characteristics of poor quality gems.
It's an excellent idea to line up several sapphires next to each other during the decision process to better see the differentiations in color, quality of cut and light reflection.
Lower priced sapphires come in a spectrum of colors, ranging from purple, yellow and green to pink, with very unusual pinkish-orange sapphires, called Padparadscha, often more expensive than the finest deep blue sapphires because of their rarity.