A sticky stem - advice needed!

[Mister Moo]

I don't think I have had a stem that wouldn't come loose after 30-40 minutes in a freezer, per Tobias Lutz advice.

If it is a screw-mount or you're not sure then twist gently anti-clockwise; if it is not a screw mount, twist gently clockwise. In both cases hold the wooden shank or stummel portion firmly as you twist or you might snap it off. Anyone who ever snapped a shank when removing a lock stem said it was easier to do then they expected. If torque enough to remove a snug bottle cap won't release it, quit, freeze again and try again. That aluminum-looking ferrule sure looks like a screw-in stop. I'm betting left turn to remove.

Any other nomenclature on the pipe besides "Chelsea"?

If that won't do it, take two aspirin and come back in the morning. When cold won't work then there are some heat-expand options. Nobody ever broke a pipe being too patient or too careful, by the way.