This video shows how to make a double sided coin ring down to a size 5 using a state quarter.

You can quench any Non Ferrous Metals (which is what a quarter would be made of) during the annealing process. Some metals (I.E. silver) tend to crack from the sudden temperature shift and as such most jewelers will utilize a steel plate to rapidly cool it before working with it (takes about 1 - 2 minutes for something the size of a ring). Also that is not firescale which he is talking about (he calls it Jewelers Scale, Silver Scale) that is only the oxidization of the metal. Firescale is a discoloration of the metal that won't go away with merely buffing it out and it tends to look slightly yellow compared to the rest of the piece, that is typically from overheating it to the point where the copper in a material turns to cupric oxide and turns a slightly red / yellow color. Either way this video is worth watching because it goes through the basics of a coin ring very well.