This is a rare, bronze, Viking Omega brooch from the Medieval era (c1400). It measures 5.5 x 4.5cm.
These brooches are called Omega because of the round shape of their heads. This one was excavated from a field near York and has been in a private collection for many years. It hasn’t been cleaned so it has a great deal of encrusted verdigris – it’s how it looked when it was first excavated after more than 600 years in the ground.
This is a wearable piece, even after all these centuries, although naturally this should be done with caution.