Here's how I made them. I got some wooden circles at Hobby Lobby and some Run 'n Buff (I love that stuff).
Just apply a little Rub 'n Buff and well... rub. I would have used gloves if I had some. It washes off with soap so I wasn't too worried A little goes a long way.
I used my silver Sharpie to St. Patrick's-asize the coins. My kids loved this part too.
I hope you make your own St. Patrick's Treasure!