Most people are aware that diamonds are graded for cut quality, polish and symmetry (with an excellent grade in each category forming the well-known “Triple Excellent” or “Triple X” rating) but it’s rare that a colored stone is graded for anything beyond clarity (and many colored stone vendors will not even provide that.) Finewater has always provided a clarity grade but we feel that a cut quality grade would also be useful, so we will be adding it to all of our gemstone listings as time permits. There are no internationally accepted cut quality standards for colored stones, so our cut grade will encapsulate several factors such as proper proportions, meetpoint accuracy, symmetry, and polish (which includes scratches, blemishes, chips, etc). Check out our previous blog articles on these qualities and how to evaluate cut quality excellence for yourself.
We now have a Graduate Gemologist at Finewater Gems – me! It’s been a demanding undertaking but ultimately my most gratifying and rewarding accomplishment in a very long time. Cutting thousands of gemstones or owning testing equipment may help develop gemological skills, but it cannot come close to replicating the knowledge that’s gained in an intensive gemology program like GIA’s Graduate Gemologist program. Whether we are hand-selecting sapphires in a Sri Lankan broker’s office, negotiating spinel prices in Yangon’s steamy street market, hunting for tourmalines deep in the remote Namibian desert, or spotting fake emeralds on Bogota’s Avenida Jimenez, you can be assured that we have the gemological skills and confidence to properly identify gemstones, validate seller’s claims, and select top colors in order to bring you the finest gemstones that the world has to offer.
Color zoning, or color banding, is a term used to describe a natural color distribution that occurs in almost all gemstones, but is most common in tourmaline, quartz and sapphire. (This is not to be confused with pleochroism, which is the change of color due to different viewing directions – a topic for a future blog post!) The most common cause of zoning is the availability of trace elements during the crystal’s growth, sometimes producing variations in a single color’s intensity, and other times producing totally different colors. It is considered beneficial when two or more colors are clearly visible and show striking patterns. This is the attraction of ametrine – a mix of purple and yellow quartz, and of multicolored pink and green “watermelon” tourmaline. Sapphires that show zoning are known as “parti-color” sapphires. Some blue sapphires (especially some from Montana or Australia) have yellow growth areas, producing a parti-colored stone with shades of blue, green and yellow after cutting. Pure blue/yellow bi-color combinations are rare in sapphire, as are other such distinct color combinations. These unique sapphires are not available commercially and are perfect for those looking for a gemstone that expresses their individuality.
Color change is one of the classic gemstone “phenomena”. Some of these gems display a subtle color shift when exposed to different types of lighting such as daylight vs incandescent lighting. For example, a garnet that appears pinkish-red in daylight may look purplish-red in indoor lighting, but since red is the same basic hue it’s not considered a true color change. A true color change entails a change in the hue (think of the distinct colors in a rainbow – purple, red, orange, yellow, green, blue and violet). Examples include the green to purple change in an alexandrite chrysoberyl, or the blue to purple change that’s somewhat common in Ceylon sapphires. It’s thought that the elements vanadium or chromium play a role in most color change gems, causing a slight alteration to the gem's crystalline structure and thereby affecting the color absorption of the light transiting the gemstone. Besides chrysoberyl and sapphire, color change phenomena can sometimes be found in diaspore, spinel, garnet and tourmaline. We love color change - it's like two gems in one!
Peridot is a type of silicate mineral known as olivine, and is most often formed underground and brought with the surface with volcanic activity. In Hawaii, peridot has historically represented the tears of Pele (the volcano goddess of fire) and very small peridot grains can be found on some Hawaiian beaches. Peridot can even be found in some pallasite meteorites! While the mineral olivine is quite common, gem quality peridot is rare. Today the primary source is the San Carlos Reservation in Arizona, but other sources include Burma (Myanmar), China, Tanzania, Sri Lanka, Afghanistan, and more recently, Pakistan, where large flawless crystals with excellent color have been found. The finest color is a rich vibrant green with a slight yellowish tint known as “apple green”. Peridot is an affordable and popular gemstone, and because it has a Mohs hardness of 6.5-7 it can be used in all forms of jewelry.
Did you ever wonder why two similar gemstones often show a difference in brilliance, scintillation and dispersion, even with the same material and same cut? Commonly known characteristics like cut, clarity or refractive index are all important, but it’s a little understood characteristic called luster that plays a critical role. What is luster? Luster represents quality of the polish (reflectivity), which depends on both the material and the polishing agent. Luster is often confused with brilliance, but these are two completely different characteristics. Generally speaking, hard materials such as metallic compounds or diamonds have the highest luster, and soft materials such as amber have low luster. Pearls have, of course, a “pearly” luster. A high-quality polish facilitates refraction and dispersion at a molecular level at the gem’s surface, subtlety but critically improving the appearance of the gems.
There are two major groups of polishing agents – oxides and diamond. Oxides such as cerium, alumina and chromium have their use for specific purposes (quartz is commonly polished with cerium oxide), but most other stones are successfully and quickly polished with various grits of diamond. Large diameter diamond grits such as 320 or 600 are used for rough cutting, fine grits such as 3000 or 8000 are used for pre-polish, and extra-fine grits from 50,000 to 100,000 are used for polishing. 14,000 is often used as a final polish in overseas cutting houses because it’s fast, but it leaves fine scratches and a “greasy” look on the facet surfaces that can inhibit refraction and dispersion. A 100,000 polish takes more time and skill, so it’s often used only for gemcutting competitions. Many cutters will say that customers can’t tell the difference in polish, but we disagree! All Finewater-cut stones except quartz are polished with 100,000 grit diamond, so you can always be assured of the finest possible polish and luster.