I know about a process of Annealing where a crystalline solid is heated to its melting point and then cooled rapidly so as to form amorphous solid which has random crystallite in uts structure.
But how is the reverse done. How amorphous is converted to Crystalline. Does it have to do anything with the fact that glass panes look milky after long time. Almost all Indian textbooks have this fact written in one of the chapters.
It is only a question of time. Crystalline substances are more stable than amorphous substances. So when heated to near its melting point, any amorphous substance has from time to time the possibility of rearranging its atoms and molecules in a crystalline order. The barrier separating random order and crystal state can, contrary to the general practice, be exceeded for a small minority of energetic atoms and molecules, according to Maxwell theory. And once a crystalline arrangement is started at some point of the solid it is more stable. So it will not go back as easily to random structure. The crystalline structure will be growing and growing. Of course, rather slowly. This is how quartz crystal have been formed from silica in nature.