A Northern California failure analysis expert witness performs a glass failure analysis on broken tempered glass windows removed from a recently built Chicago Illinois high rise. Soon after construction windows in the high rise began to fail. Read Consulting which provides failure analysis services in Santa Rosa California was contracted to determine the cause of failure. A portion of each window containing the failure origin was preserved and sent to the Read Consulting failure analysis laboratory. The failed windows were deconstructed and the fracture surface at the origin was examined microscopically. Root cause failure analysis demonstrated that the high rise windows failed as a result of nickel sulfide, NiS, inclusions in the glass. One photo above show a representative window failure. The other photo is a 500X photomicrograph (taken with Nomarski optics) of one of the NiS particles. It is a 170µ diameter spherical particle. The arrows indicate the direction of the spreading crack.