Producing durable glass tile begins with quality raw materials and/or recycled cullet (broken or waste glass, usually added to new material to assist melting in the making of glass). Mineral formulas are blended with silica sand and melted thoroughly to eliminate excessive air bubbles and inclusions. Each inclusion is a potential weak point, susceptible to fracture.
Of course, glass tiles are manufactured many ways, and whether a tile is cast, slumped, or fused, the important thing to know is that all glass must be annealed. Annealing is controlled cooling that relieves internal stress and prevents shattering. If the process is rushed, invisible stress remains unresolved within each tile, waiting for the perfect moment to release (shatter). This defect is undetectable by the naked eye, but when translucent glass is viewed through polarized lenses utilizing a light table, it is very easy to see any stress that may be present.
Photo courtesy of Alpentile, LLC; photography by www.michaelwoodall.com; designed by Amy Denny; tile installation by Luke Denny; tile by Oceanside Glasstile