Mystifying problem. Two heavy porcelain bowls I've had for years have got stuck together, one inside the other. They were stacked in the cupboard as usual, I got them out one day, and found they were jammed together, at a slight angle. Have tried washing them, leaving them in water, putting cooking oil in them to grease them, and they won't budge.
No idea why this has happened now.
Any ideas what to do about it?