Very similar to a Master Glass Marble.
Master Glass Marbles did not stand up to the quality of Master Made Marbles, one of the very early USA Machine Made marbles.
There is a very distinct difference between the two.
Yours could pass as a Master Glass "Brushed Patch"--a later marble made in the USA but the quality is far beyond what they made.
Yours show a distinctly clear glass with an intended patch with some of what I would call some grey inculded.
I do not get the argument here because I would trade ten of my Master glass marbles for one of yours--the quality is evident, yours is better.
If you want some Master Glass marbles--just PM me.
I am willing and able to send you some.
I would love a trade for some Whisplers from a collecting friend overseas.
Marble--On!!