Specifically, it's corundum that's blue because it's got titanium and iron impurities. Anyone trying to sell you a "white sapphire" (or this "sapphire" glass)

Specifically, it's corundum that's blue because it's got titanium and iron impurities. Anyone trying to sell you a "white sapphire" (or this "sapphire" glass) is trying to pull the wool over your eyes. I can see why, though - it's an easier sell than calling it just corundum.