At Stuller, we have been analyzing white gold problems for more than a decade. Years ago, we set up a metallurgical lab for harness testing and grain size analysis to gain an in-depth understanding of these problems. Our current understanding is the following:

During the first 40 years of this century, platinum was the preferred metal for wedding and engagement rings, and was almost always used to enhance the beauty of diamonds and other gemstones. In 1942, the U. S. Government banned the use of platinum in non-defense related industries. Jewelers needed a new material, white in color, to replace platinum. A 14K nickel gold alloy was chosen as the setting material.

To make yellow gold turn white, you must add between 6.5 percent and 13 percent nickel to the gold alloy, and reduce the copper content accordingly. Most setting manufacturers use 11 percent nickel content.

In metallic materials, atoms are arranged into unique crystal structures. The evidence of these crystal structures is seen in the collection of grains which compromise all metals. Each grain is a collection of atoms arranged in the same structure with a unique orientation. Yellow gold alloys contain copper, silver and gold. The crystal structure is uniform and is all face-centered cubic. Yellow gold alloys are single phase alloys. Nickel is not as soluble in gold as copper and silver. Two different crystalline structures are present in nickel-white golds, and it is a two phase alloy. There is evidence that the two phases present in nickel-white golds help promote stress corrosion cracking in the alloy. Stress cracking and stress corrosion are the problems that occur with nickel white gold alloys when they are placed under mechanical or thermal stress. Cracks occur at the grain boundaries, over time , and in the presence of corrosive chemicals (chlorine in most cases), these cracks propagate along the grain boundaries in the stressed areas until the metal fractures.

Where does the stress come from? First, it comes from the heat of soldering. Second, it happens when the prongs are notched and then bent over the girdle of the stone. In out tests, notches made with a v-shaped wheel caused cracking in every sample. Bending the prong tip creates tensile stress on the outside of the prong tip, and compression stress on the inside of the prong tip. These stresses enhance the stress cracking problem.

If the presence of any corrosive chemical is added, we find accelerated stress corrosion cracking occurs. Failure of prong tips can be measured in days.

Stuller recommends these solutions:

1. Use Platinum settings whenever possible. Platinum exhibits none of these stress-related problems. It is more durable and has negligible spring back.
2. Work with your jeweler or trade shop to minimize the potential for stress cracking by using these techniques:
   1. Use a setting or ball burr to cut seats; make sure your tools are sharp and use a lubricant to avoid generation heat; burnish the seat after cutting. Platinum is the metal of choice for setting a stone of financial or emotional value.
   2. Do not bend the prong tips back when inserting the stone. Bend the prongs forward slowly and do not force the tips in to the stone. Use alternate-side tightening procedures.
   3. Stress relieve the ring after setting (diamonds only) by placing it in an oven at 650 degrees Fahrenheit for 35 minutes.
3. Educate your customers to avoid contact with corrosive liquids, solids, or gasses. In particular, spas and swimming pools are undesirable environments for gold jewelry. Encourage them to come in for regular cleaning, as notches can trap concentrated deposits.
4. Suggest that an appraisal be done for the piece of jewelry, and that it be included on their homeowners’ insurance. This insurance is readily available and usually inexpensive.

By keeping these facts in mind, both you and the consumer can have “Stress Free” jewelry.