A system and method for growing diamond crystals from diamond crystal seeds by epitaxial deposition at low temperatures and atmospheric and comparatively low pressures. A solvent is circulated (by thermal convection and/or pumping), wherein carbon is added in a hot leg, transfers to a cold leg having, in some embodiments, a range of progressively lowered temperatures and concentrations of carbon via the circulating solvent, and deposits layer-by-layer on diamond seeds located at the progressively lower temperatures since as diamond deposits the carbon concentration lowers and the temperature is lowered to keep the solvent supersaturated. The solvent includes metal(s) or compound(s) that have low melting temperatures and transfer carbon at comparatively low temperatures. A controller receives parameter signals from a variety of sensors located in the system, processes these signals, and optimizes diamond deposition by outputting the necessary control signals to a plurality of control devices (e.g., valves, heaters, coolers, pumps).