A container between the output of a melting furnace wherein the molten mass is also refined, such as for glass, and the ducts to a plurality of forming machines comprising a larger first zone and a plurality of smaller second zones corresponding to each forming machine, in which container the molten mass is controlled in temperature above and below its liquid level as it flows through the first and second zone toward a forming machine so that the cross-sectional area of the molten mass at the outlet duct from each second zone has substantially a uniform temperature. Each zone is provided with temperature control means for both heating and cooling, such as burners and/or electrodes above and below the surface of the molten mass in the conditioner, and fluid jets and/or hollow ducts or panels engageable with the outside walls of the conditioner, so as to establish the desired uniform temperatures throughout the depth and width or cross-section of the molten mass flowing from each outlet duct of the conditioner and to minimize as much as possible convection currents in the conditioner.