Primary Test: This imitation of opal has been around for decades. It is usually glass embedded with foil and then cut en cabochon. Magnification is all that is required to identify this material as a cheap imitation of opal that is found in costume jewelry and only the cheapest of efforts to emulate an opal.
Secondary Tests: None needed
Repair and Setting: No heat, no ultrasonic and no cleaners. Material is usually plastic or glass with plastic ribbon fillers. Very susceptible to heat and cleaning solutions.