The Four Leaf Clover Door Knocker is sand-cast in solid bronze and is finished with a high gloss polish. Brass and bronze are copper-based alloys. The yellow brass alloy used in many of Michael's designs contains 70% copper and produces a warm, traditional brass look. Red bronze contains almost 85% copper. This additional copper content gives the bronze alloy its rich, reddish undertone. The mirrored finish of polished brass and polished bronze is achieved through varying degrees of sanding and buffing. Michael uses these techniques to highlight or accent the raised areas on a piece.