1821 D.3-D (Z.4-AI) come from the Ski Nose family. All XRF-analyzed examples have been found to be struck on brass planchets. Most have medal turn, such as this example.
 
Surprisingly, this is the first time I've offered this variety here. This example boasts VG/F details, and has quite nice surfaces for this variety. The planchet is also thick and perfectly round.