That's REALLY interesting and good to know, Leni!
I was once desperately trying to decipher how a big beer stein had been decorated, without the benefit of a magnifying glass, or glasses which allow me to focus on anything remotely close to me, so I was feeling it with a fingernail, (that most useful of glass investigating tools!) and the design stood proud - although it kind of looked as if it shouldn't.
It was a lovely design - a stag in a forest, with mountains behind, loads of detail, I simply couldn't decide how it had been produced, now I know. :kissy:
(sorry, it's gone from the charity shop where it was, I had you in mind when I was "examining" it)