That "patina-oil" look also points to it being in the sun. If you are ever in the desert, you will find lots of broken glass that has gotten that look. It's pretty, imo. I've collected quite a few. Some call it "desert glass", the pro's call it "solarized" glass. It can fool you. The first 4 opals that I found in the desert were not opals, but opalized desert glass.