rearview mirror button removal

[Jack4159]

Me again,
This is a pic of the button(not sure if that is the right term) on the front windscreen that the rearview mirror mounts to and pivots on.
As you can see I need to get this off to clean it up, have found some info online that suggested a butane torch was the go but I am fearful the heat may crack the windscreen, which amazingly looks to be the original.
Is there a preferred way to get this button off?
Thanks as always.

[68blk500c]

Forget the torch, use a heat gun and slowly raise the heat. A little pressure should make it release.

Sometimes in the cold, they just fall off.

[Poor Ron]

Use chalk or a marker, mark the outside of glass for proper placement.
Also mark the inside of the button top or bottom with an arrow.
Yes; heat gun is the way.