Some opals absorb water and lose color temporarily. If you'd like to narrow this down, let me know: What is your budget range ? Do you have a favorite color (Fire red, ocean blue, etc.)?
Used to make cheap Ethiopian opals look like Black Opals. how to buy opals
Tiny cracks on the surface. These can eventually break the stone. Some opals absorb water and lose color temporarily
Too perfect. Patterns look "snakeskin" or repetitive. how to buy opals