Sue, that is such a good question and I've never been able to find consistent answers. I am never sure if I am using the right word -- opal, opaline, opalescent. The French and Italians refer to the glass with amber fire as opaline or opalino (e.g., Veritable Opaline). But others call that opalescent. I've read some places that opalescent is the opaline glass that has a pearlescent quality. But other places I have read what you mentioned.
So I have always been confused.