A common method for making brooches and other jewellery was the 'lost wax' process:
1.take a clay mould of an already existing brooch
2.make a wax model from that mould
3.touch up the wax model - making changes as you see fit
4.make a clay mould from the wax
5.cast another brooch
A good paper on the subject can be found here: 
more information needed... Some images available for this topic.