Here's a thread for the benefit of newbies and maybe not so newbies.
What examples do you have and/or know about of marbles which you think could be mistaken for old?
Here are a couple of my favorites, these pix from Schusserland.de.
Clownfish sometimes taken to be Master:
And not sure of the name, but some like the two-seamers in this batch have been questioned in the past as possibly vintage: