Question

when gypsum converted into pop

Answer 1

If we heat gypsum at 100 ° then POP is formed and if this POP is kept in wateror in moisture it gets converted into gypsum again

Answer 2

After wetting or moisturizing POP plaster of Paris gets converted into Gypsym Ca SO4.2 H2O... It gets set in an hour or so. When it dries we get a solid sculpture like substance now. It gets hardened.

The original powder state of POP may not be obtained as it is.

I did not understand the question fully... POP is made from Gypsum only. There is little chance that we cannot make POP from it..