Despite the vulnerability of the low-karat golds to this phenomenon, it is not widely observed today, which tends to suggest that the manufacturers are at least aware of the potential problem and take steps to minimize its occurrence.
Stress corrosion cracking can occur in some lower karat-gold alloys (8–10K and less frequently in 14K, but particularly nickel-white golds) due to the combination of a corrosive agent and an applied or residual stress. The corrosive agent is typically a chemical in the local environment.
Cracking or, in the worst cases, spontaneous failure only occurs by this method in the presence of both a stress and a corrosive agent. It may happen during the following:
Due to fumes from pickling
Exposure to chemicals during consumer use, even after many years of satisfactory service.
The mechanism of stress-corrosion cracking is complex and not discussed in full here.
Causes of stress
The residual stress is commonly introduced during manufacture. It is important to stress-relief (or fully anneal) potentially susceptible alloys before the point of sale. A suitable treatment for stress-relied anneal would be 250-350°C/480-650°F, typically for 30 minutes, and has little effect on hardness or grain structure.
Unfortunately, stresses can also be introduced in service with the customer (for example, chains stretched by children pulling them) or by the jeweler when rings are re-sized without a subsequent annealing treatment.
Crack initiation is likely at a defect, scratch, or even a stamped mark, where stress is concentrated in the surrounding material.
Causes of corrosion
Chlorine or chlorides are a major agent; acids and pickling solutions are the usual source at the manufacturer.
For the user, the list is almost endless: detergents and household cleaning fluids, inks, swimming pool water, sea water, and coastal atmospheres, some foodstuffs, perfumes, deodorants, and human sweat can all act as the source of corrosion.
The failure usually manifests itself by a characteristic intergranular fracture. The susceptibility of alloys to stress corrosion is particularly determined by the composition and by metallurgical structure, but the subject is a complex one with initial attack determined by local differences in composition and initiating at a defect or stress raiser.
For further discussion, see:
W.S. Rapson, “Advances in Knowledge Relating to Gold Alloys and Their Use in Jewellery,” The Santa Fe Symposium on Jewelry Manufacturing Technology 1995, ed. D. Schneller (Boulder: Met-Chem Research, 1995): 65-82.
G. Normandeau, “Stress Corrosion Cracking Evaluation of Cast Products and Stamped Four-Claw Settings,” The Santa Fe Symposium on Jewelry Manufacturing Technology 1991, ed. D. Schneller (Boulder: Met-Chem Research, 1992): 323-352.
J.J.M. Dugmore and C.D. DesForges, “Stress Corrosion in Gold Alloys,” Gold Bulletin 12, no. 4 (1979): 140-144.
S. Grice, “Failures in 14Kt Nickel-White Gold Tiffany Head Settings,” The Santa Fe Symposium on Jewelry Manufacturing Technology 2002, ed. E. Bell (Albuquerque: Met-Chem Research, 2002): 189-230.
C.C. Merriman et al., “Environmentally induced failure of gold jewelry alloys,” Gold Bulletin 38, no. 3 (2005): 113-119.
C.W. Corti, “Jewelry —Is It Fit for Purpose? An Analysis Based on Customer Complaints,” The Santa Fe Symposium on Jewelry Manufacturing Technology 2018, ed. E. Bell et al. (Albuquerque: Met-Chem Research, 2018): 163-176.