The challenge in making glass is that sand’s main ingredient, silica (silicon dioxide), melts at extremely high temperatures— over 1,700°C, far higher than anything an open fire or primitive furnace could manage. However, add a so-called “flux” to the mix and you can persuade the silica to melt and flow (flux) at much lower temperatures. Indeed, choose the right flux and not only will it reduce silica’s effective melting temperature, it will also sop up the impurities in the glass, helping improve the final product.
