Iridescent mosaic tiles are primarily made from glass. During the glass firing process, iridescent water is fused with the glass, creating a dazzling rainbow-like effect on the surface. This effect mimics the natural iridescence seen in polished seashells, though different types of shells display various levels of iridescence. However, through glass craftsmanship, this radiant effect can be intentionally replicated, allowing any color of glass mosaic tile to adopt this magical quality.