Professional Jeweler Archive: Durability Issues for Lab-Created Moissanite at the Bench

January 2003

Professional Bench/Manufacturing Up Close


Durability Issues for Lab-Created Moissanite at the Bench

As the use of this stone in fine jewelry grows, here are some tips for working with it at the bench


Bench jewelers are required to quickly work through their assigned workbox of repair, reconstruction and custom orders daily. The profitability of the department depends upon a speedy and professional outcome. Among the details slowing the bench process and productivity include the unmounting of gemstones. This is particularly true when bench jewelers are uncertain of the extent to which a stone will take heat or withstand general stress when subjected to normal bench procedures.

This article examines issues related to the durability of lab-created moissanite. Durability can be thought of in two general categories, hardness and toughness. Hardness is the ability of a stone to resist scratching and abrasion, and toughness relates to its resistance to breaking, chipping or fracturing.

General Characteristics

Moissanite, created by Charles & Colvard, ranks 9.25 on the Mohs hardness scale. It’s cut in round brilliants and most fancy shapes. Sizes range from 3-13mm.

The cut of a gemstone, along with the traits of its internal characteristics, largely influences the outcome of setting and handling without damage. Charles & Colvard exclusively manage the cutting of created moissanite to exacting proportions. Thin and wavy girdles, excessively shallow crowns with small tables and other features characteristic of routine commercial cutting that pose potential problems for stone setters are not present.

The material is distributed in higher qualities with no eye-visible inclusions. Internal characteristics requiring magnification are thin white needles and very fine reflective stringers. There are no significant inclusions or planes of weakness due to prominent cleavage that would contribute to vulnerability when setting.

Setting

While created moissanite is of superior durability, professional setting procedures must be practiced. When setting stones, a bearing – which will seat the stone – must be created regardless of the stone’s shape or setting style. To minimize potential damage, bearings must conform to the stone’s profile to provide a level and secure seat free of sharp uneven edges.

This bearing has been prepared in prongs before setting. Its shape conforms to the proportions of the stone. Notice the combination of the crown and pavilion angles is about 70.&Mac251; A 90&Mac251; setting bur was used to create the seat. Once the stone is seated in the bearing, the prongs are bent over to secure it in place. This preparation will provide a firm, secure seat that will hold up during normal wear.

While lab-created moissanite is harder than all other stones (except diamond), its facet junctions can still be vulnerable to heavy, crude unorthodox filing. When finishing prong shapes by filing, the file must have a “safe” edge, one that’s been ground and polished smooth. Proper use of cup burs for finishing prongs will yield no problems. Avoid abusive techniques such as excessive force in combination with high speeds as abrasion will occur.

This bearing does not conform to the stone’s profile.

1. The angle of the lower part of the bearing doesn’t match the angle of the pavilion.

2. Large gaps will be obvious at the girdle.

Breakage is likely when trying to set any stone in a bearing prepared like the one illustrated. If it survives the setting process, it’s likely to break during normal wear. This general rule includes created moissanite stones.

When setting these stones in channels, be mindful of contact with an adjacent created moissanite. As with any stone, if one is forced into the bearing and contacts the adjacent stone, it may cause one or the other to break.

Prefinishing and Polishing

After the setting procedure is concluded and the prongs and channels are filed, the next step is prefinishing and polishing. Most rubber wheels contain silicon carbide, diamond or other abrasives that will scratch created moissanite.

Prefinishing rubber wheels ideal for settings containing these stones are pumice wheels or pumice-impregnated silicon wheels. There’s enough pumice abrasive content to perform final prefinishing but won’t damage the stone.

When used appropriately, polishing compounds and ultrasonic cleaning have no adverse affect on created moissanite. To avoid abrasion, make sure created moissanite does not come in contact with other moissanites while in the ultrasonic cleaner or when you’re performing other cleaning and drying functions.

Breaking a moissanite when coming in contact with adjacent stone.

Stuller has been setting all sizes and shapes of created moissanite for the past several years. “While setting thousands of these stones in all styles of mountings, damage during the setting process has been limited to the princess cuts,” says Brett Northcutt, director of stone setting at Stuller. The crown angles of the princess cuts are shallow and the corners are sensitive and require extra time, he says. The pavilions on oval created moissanite can be thick and steep, often requiring a larger stock setting than normal outside dimensions stipulate, Northcutt advises.

He cautions that prefinishing after setting must be done with select rubber wheels because some containing silicone carbide and diamond abrasives will scratch the facet junctions. Overall, Northcutt says, he finds lab-created moissanite a desirable material to set because of its superior cut, durability and hardness.

For information related to working characteristics of created moissanite at the bench, call Mark Mann at (406) 961-4426 or (800) 210-4367, ext. 251. Lab-created moissanite educational content is sponsored by Charles & Colvard, (800) 210-4367.

– by Mark B. Mann

Illustrations by Lainie Mann
© 2002 Visual Communications
(406) 961-4426

Copyright © 2003 by Bond Communications