Abstract: A substantially-isolated/controlled, limited-volume, gas-filled space (e.g., 113b) is formed over at least one free (open) surface of flowing molten glass in a manufacturing line used to produce glass sheets (137), e.g., a manufacturing line employing the fusion process to produce glass sheets suitable for use as substrates for liquid crystal displays. At least a portion of the space comprises a platinum-group metal, e.g., a platinum-rhodium alloy, which can serve as a source of platinum-group condensate defects. The use of the substantially-isolated/controlled, limited-volume, gas-filled space substantially reduces the level of such platinum-group condensate defects in the glass sheets, e.g., by more than 50%.