Please keep me posted. I found a square one with a crested helm in the middle of it , and the oxidation appears to be very similar. I called mine square , but it it by no means concentric , and it has scalloped edges. I am also very interested in the age on it. Ours seem to have a similar metal in common , however there was evidence of some brass plating remaing in the lowest recesses of my button. However, with a very delicate cleaning, we began to notice we were loosing this plating , and halted there. This appears to be very, very old , and very far out of place in regards to the area it was found in.