Milners Plaque variations?

[Warren63]

Hi all. I’ve always assumed safe plaques were either cast brass (heated & liquefied, poured into a mould) or pressed (thin sheet stamped onto/into a form). These three Milner plaques are a bit confusing! I would’ve thought that the all black one was cast brass because of the depth. But the small unpainted one seems hard to tell if it’s cast or pressed. It’s about a third of the thickness of the large black one, but still seems a bit too thick to be be pressed because of the thickness and the fact there’s no relief to the back. The red and black one I’ve just acquired. The paint was in a terrible condition so I had to strip it. Unfortunately it was so detailed it could hardly be seen without the pains so I had to repaint it (nightmare). It’s similar in type as the small unpainted one but even thinner again and no relief to the back. How were they made?