You guys give me a lot of reading to do

To my knowledge;
Officially, only glass from France, made in a certain period in the 19th century should be called opaline.
Even though pieces were made later, and in other countries. They might even be made with the same receipe,
OFFICIALLY it's only French.
It indeed can be either shiny or matte. It can also be a little translucent, or opaque.
The translucent version is called 'bulle de savon' opaline, which is a little see-through.
It can be milky/soapy or not at all. And it doesn't always have the fiery glow. Many do. Many don't.
There are some nice translucent pieces to find online, called 'clair de lune'. (Moonlight)
Just like opaline in general, not all the pieces described a clair de lune are so in fact.
Now to make it more complicated;
I have no idea how to see or to know. I have a opaline glass box, made by Baccarat.
In the book "les Opalines", by Christine Vincendeau, it's described as 'demi-cristal d'opale savonneux'.
That's something like 'soapy opal half-crystal'.
Either in this book, or the other one I have (L'Opaline Francaise au XIXe Siècle, by Yolande Amic)
seen that there are receipes in it. For how to get certain colors.
I haven't translated these books, and I don't speak French :p
It's also known that french opaline become more popular, I think, around 1835.
Anyway, in the Napoleon III era. It was then when new colors were created, and the production was increased.
So some later pieces could technically be dated after 1830 on color alone, if you'd knew all the facts properly.
(By the way I don't own any other books then these 2)
My newest miytery is how to tdistinguish Russian and French opaline from each other