Last winter, my mother stored a couple of planters by putting one inside the other. The planters are embossed with a decorative pattern on the outside and smooth on the inside, with an inward-curving lip at the top.
Now it's the season to bring the pots out and put plants in them, but these two planters refuse to be pulled apart. They were stacked together when temperatures were close to freezing; now it's always at least 60ºF outside, and I believe the inside planter has expanded so that the decorative pattern has a greater diameter than the inner lip of the outside planter.
My father and I have tried the macho approach of pulling them apart with all our strength, but without success. I also tried storing them in a refrigerator for a while, but they didn't contract enough to pull apart (assuming my temperature theory is correct). I would like to try putting them in a freezer, but we don't have a freezer that's big enough.
How can I detach these planters without busting one of them in half?