Do you make your own bath bombs or fizzies?

[PrincessMommy]

my kids bought me a couple of Lush brand bath bombs for Christmas... oh my!  They were wonderful, without being overpowering.  But they are SO expensive.

 

I want to make my own but am unsure about some of the recipes I found online.   Several of them have liquid (water or witch hazel) in the ingredients..  Wouldn't make make them start fizzing before molding them? 

 

 

[dirty ethel rackham]

I was at a craft fair where a bunch of kids were selling their own homemade bath bombs.  I didn't ask them how they made them, but they apparently worked because they had repeat customers.  I would love to use them, but that would mean me having to scrub the tub before taking a bath.  No very relaxing.