Synthetic ruby created by dissolving alumina (Al₂O₃) in a molten flux and allowing the ruby to crystallize out.

Various companies have produced rubies using flux methods, for example Kashan, Ramaura and Chatham and these synthetic rubies are sometimes marketed under their company names.

Some manufacturers seed the flux with small ruby crystals, others allow the ruby to crystallize out at random.

Lower temperatures are needed for flux growth than for flame fusion - in some fluxes temperatures as low as 800�C (1,470�F) are enough to dissolve the alumina, but in general temperatures over 1,200�C (2,200�F) are used to produce higher-quality crystals. The temperature must be maintained for a period of between three and twelve months in order to grow useful-sized crystals.