Hi there,
Thank you Frank, Flying Free and others.
This one has a purple-ish layer in between.
Here are some more pictures about the cased layers. There are some faint lines in the purple layer and a spiral line in te upper clear glass layer that you can feel.
My base is also not age scratched but has three little chips.
I also think it should be placed upside down because of the light effect.
Kees