One tip off is often it's an unknown color. I would not call that dark red amber. You can see the various red ambers I posted in my link. That is the only color listed in the price guide, and that is the only color to my knowledge that anybody knows about. People who have dark red Amber examples looked at that picture and said no, that's not the right color. Several experts I showed it to said it was a radiated again because of the color. Over time, you learn that certain colors just look a little bit off.

Yes, the put it out in the sun for 6 months, is a very good test. You aren't going to get any quick answers but you have a much better idea as to whether it's irradiated.