An apparatus and method for casting metal strip include a moving chill body that has a quench surface. A nozzle mechanism deposits a stream of molten metal on a quenching region of the quench surface to form the strip. The nozzle mechanism has an exit portion with a nozzle orifice. A depletion mechanism supplies a low density atmosphere to a depletion region located adjacent to and upstream of the quenching region. The quench surface is heated to a temperature that substantially prevents precipitation of condensed or solidified constituents from the low density atmosphere onto the depletion region.