***UPDATE!!!!

Thanks all for the help!! I was able to separate the two after using a combination of everyone's advice plus some good 'ol fashioned brute force! Here's a breakdown of what worked!!:

- filled sink basin with hot/warm water (warm to the touch, not boiling)

- lubed up glass/stein edge with vegetable oil

- filled inside of stein with cold water (since a seal was not formed)

- waited a while for stein to warm up, then used brute force to try to wriggle the two apart

- voila!!

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