I'm looking at a glass "recipe" that heats the raw ingredients to melt at 1550C. This seems to present a problem in that the raw ingredients include: Al2O3: melting point = 2072 C MgO: melting point = 2852 C And even SiO2 (the primary ingredient) has a melting point (range) of 1600-1725 C . So I'm puzzling over how this can possibly work. Yet apparently it does work, as this is a real recipe. I can blindly go ahead and do it, but would really like to understand how & why this can be. I understand that impure crystals have lower melting points. But in searching these forums (and the web in general) I can find no discussion of deltas that big -- (MgO melting a full 1300 C lower than its pure MP???). It seems.... surprising. [Furthermore, the recipe seems to assume no such requirement of impure ingredients.] So I figure I must be missing something. Probably something very fundamental. My only idea is that maybe those higher-melting-point ingredients are not really melting. Maybe they are just dissolving in the lower-melting-point SiO2 liquid? (But even then, 1550C doesn't seem quite high enough to melt the SiO2 -- though with impurities, I guess it could.) Is that it? Or am I indeed missing something? Thanks much!