California glass expert was asked to perform a glass failure analysis on a glass door that failed spontaneously, The failure analysis lab located the failure origin. The glass experts then examined the fracture surface at the origin, and they determined that the root cause of the failure was a nickel sulfide particle. The failure origin magnified 200X is shown in the color photograph. This photo-micrograph was taken using Nomarski interference contrast. In it one can see that there is a spherical particle at the origin. Using energy dispersion spectroscopy (EDS) the elemental composition of the particle was determined. The chart shows that elemental composition of the particle is nickel (Ni) and sulfur (S). After the thermal tempering process, this particle, over time, went through a post temper phase change that generated tensile stresses and cracking which eventually caused failure. It is important to note that the particle is composed of only two elements, Ni and S.