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!