Abstract: A microwave refining and melting furnace for the treatment of dissolved or solid products includes a first waveguide traversed by a microwave beam generated by a generator coupled to a first end of the first waveguide. The first waveguide is provided with a material supply orifice located at an upper part thereof close to a first end of the first waveguide. The first waveguide has at a lower part thereof, close to a second end, an overflow lock of variable height making it possible to define a retention volume for the materials, which have been progressively melted by a continuous flow along the lower wall of the first waveguide, from the reception point thereof in the first guide. A second waveguide is connected to the first waveguide for refining the materials.