What Makes a Diamond Have Appealing Contrast?

A diamond with positive contrast has a distribution of bright and dark facets that change as the stone is rocked from side to side. The diamond's dark faces highlight its neighboring light faces and contribute to the stone's overall brilliance. Very large diamonds may actually have less attractive contrast than medium sized diamonds because large diamonds' facets are large and separated one from another. Tiny diamonds, on the other hand, may have great contrast but it will be difficult to appreciate it because the faces are so small. Three additional factors contribute to a diamond's contrast, its depth, head interference, and symmetry. Diamonds that have a deep pavilion leak light from the bottom and so most of the facets will appear dark. Diamonds that are shallow leak light from the sides, so the stone will have less contrast. Diamonds with the perfect (Tolkalsky) cut also have dark facets, but they are fewer in number, triangular, and contributory to the diamond's appealing contrasts. Head interference also influences diamonds' contrast. If the stones are cut so that light going in comes right back out to the viewer, than the viewer's head, which blocks the light source, will make the diamonds appear dark. In well cut diamonds, light coming in from the sides will be reflected back into the eyes of the viewer giving the diamonds a shiny appearance. Symmetry also plays an important role in creating beautiful diamond contrast. A well proportioned diamond creates the most beautiful contrasts.

What Makes a Diamond Shine?

Diamonds shine because their special cut creates a state called "total internal reflection." That means that the light entering from the top will reflect off two facets before returning back out the top. This special effect is created by skillful diamond cutting and is based on diamond's high refractive index. This high refractive index means that the direction of light bends a lot as it travels from air to diamond or from diamond to air. Because of this bend, when light travelling through the crystal lattice meets a face at an oblique angle, it will bounce off rather than penetrate through it to the outside. Generally light that enters a properly cut diamond from the top will bounce off two faces before returning to exit out the top. At this point the light is heading straight into a top facet (head on) and will emerge rather than bounce off of it as it did when it met the earlier facets. The process is so delicate because if the diamond's pavilion is cut too deep, the light will leave through one of the lower facets. If the pavilion is cut too shallow, the light will exit through a side facet. Light can enter and leave the crystal in so many ways and bounce around in so many different directions that getting the best effect is a special art. For this reason, only the most experienced diamond cutters are called upon to cut the largest and most expensive stones. ********************************************************** The refractive index of diamond is pretty high (2.417) and is also dispersive (coefficient is 0.044). Due to this fact, diamond is an important application in optics. Consider an ideal cut diamond. I explain according to the figure below. When the light is incident at an angle 1, it refracts inside and travels through the lattice. At the surface which separates air & diamond media, the incident angle 2 is very well above the critical angle (ca) and simultaneously (3 & 4) the reflection takes place at different surfaces of the diamond. Finally, the light refracts out. But diamond on the other hand has a really high refractive index (≈2.4) and because of that the critical angle for total internal reflection to occur is much smaller. So a greater percentage of the incident light gets internally reflected several times before it emerges from the diamond, making the diamond look really shiny.

Avoiding Diamond Switching Scams

Most jewelers are trustworthy and would never cheat their customers. In fact people usually fall prey to diamond switching scams because they made a poor jeweler selection. That said, diamonds can be switched (usually for a cubic zirconium) anytime the jewel is left unattended with an unscrupulous jeweler. This may include the gap between purchase and mounting, the times when a diamond ring is brought in for cleaning, repairing, remounting, etc. You can prevent diamond switching by having your jeweler plot out your diamond on your receipt. This will basically include making marks signifying the location and size of your stone's inclusions. Many inclusions are so tiny they are invisible to the naked eye. However, you should ask to see your diamond through a loupe (a small magnifying glass used by jewelers). You can also identify your stone by the grading report and or any laser engravings. If your jeweler refuses to cooperate with your request, you should take your business elsewhere. Let your jeweler know you are keeping track of your diamond's unique appearance. Come to a common agreement about the unique marks on your precious stone before leaving it at the shop. Check it when you go to pick it up. If there are any discrepancies, bring this to the jeweler's attention immediately. These steps should discourage any dishonest shop owner from trying to switch your diamond.