Diamond simulants can be made of any natural or manufactured material (right). Advanced technology has improved simulant appearance and durability and intro­duced new materials such as synthetic moissanite (above).

FRACTURE FILLING

Fracture filling, which began in the 1980s, is the most common diamond clarity treatment today. During fracture filling, a molten glass substance is infused into a diamond's fractures. The refractive index (RI) of the filler is close enough to the RI of diamond to make the fracture almost invisible.

The most obvious evidence of fracture filling is called the flash effect. It's a flash of changing color that shows up with proper lighting under magnification. To search for the flash effect, view the suspected filled fracture along its length and rock the stone parallel to the fracture plane so the background goes from light to dark. If the fracture is filled, you should see two colors flashing as you rock the stone. Yellow to orange, pinkish purple to yellowish green, and yellowish orange to electric blue are common combinations. Fiber-optic light can make subtle changes more visible.

Don't confuse the flash effect with iridescence or with the orange-colored stains caused by included iron compounds, both of which some­times occur naturally in feathers. Other signs of fracture filling include trapped gas bubbles and crackled texture in the filler.

CLARITY TREATMENTS

Most diamonds have inclusions. Some inclusions can be eliminated or placed in an inconspicuous position during cutting. Some are large and obvious enough to require more than that. The late 1900s brought many advances in diamond clarity treatments.

ANNEALING

Annealing—a controlled heating and cooling process—is another color modification method. It can follow irradiation in a two-step process that modifies irradiated color to produce brown, orange, or yellow. Pink, red, and purple shades are rare, but also possible.

Annealing, used alone, can change unattractive diamond colors m a series—generally blue to green to brown to yellow. The treatment is stopped at the desired color. It's also possible to anneal yellow to brown synthetic diamonds to more desirable reddish colors.

Heating at a later time can alter the color of annealed diamonds, so use caution with a jeweler's torch.

IRRADIATION

The first commercial use of irradiation to modify diamond color came in the mid-1900s with the introduction of the cyclotron, a giant device that accelerated electrons along a circular path. A diamond irradiated this way often had an even, medium-to-dark, vivid green, blue-green, or blue color, which hardly ever occurs in natural diamonds.

In cyclotron-irradiated diamonds, the color penetration was shallow, which caused distinct color zoning. A circular, umbrella-shaped area of color around the culet was one sign. Others were color zoning parallel to the facet junctions, a colored ring around the girdle in green, yellow, brown, and pink diamonds, and color zoning in the culet area of green, blue, pink, or yellow diamonds. If you see any of these things, you should send the diamond to a gemological laboratory for testing.

DIAMOND TREATMENTS AND SIMULANTS

Modern technological developments make it possible to treat diamonds in a variety of ways. Treatments now exist that can induce color, lessen color, and improve apparent clarity. Advances in treatment technology increase the need for improved detection techniques and stricter disclo­sure guidelines.

Laser technology has brought about new developments in diamond identification. Manufacturers can now inscribe an identification number and even a brand name and logo on a diamond. While not considered treatments for grading purposes, you might see them when you're exam­ining diamonds under magnification.

CUT

How easily and accurately you can judge the cut of a mounted diamond depends on the setting, but the characteristics to look at are the same as for a loose stone.

Either estimate, or measure and calculate, the diameter and table size, just as you do for a loose stone. The face-up method is the best way to estimate the crown angles of rounds. With fancy cuts, try to get a clear profile view of at least some bezels.

To assess girdle thickness, judge the areas you can see. Tilt the stone and look through the table for reflections of the hidden areas. Judge pavilion depth and culet size just as you would for a loose stone.

Judge finish just as you would for a loose stone. You might be able to use reflections to see areas hidden by the mounting.

To compare a mounted diamond to a masterstone, hold its table very close to the masterstone's table, but don't let them touch. Examine them together under 10X magnification.