How can the melting point of silica be lowered?

If other materials containing fluxes are mixed with silica, in the correct proportions and within certain limits, the melting point of the mixture will be lower than that of its constituent parts.

However when when a mixture of silica and fluxes melts it very quickly becomes fluid like water and would run off anything other than horizontal surfaces.

This very small range of temperature within which the silica + fluxes mixture melts presents another problem as temperatures in pottery kilns often varies considerably from one place in the kiln to another.