Check out info on resin casting. You have a mold, mix the resin with a catalyst. Whatever is in the mold gets embedded in plastic. - This link doesn't include info, but it's a reminder to go check out more info on resin casting
This homemade clay recipe only takes two ingredients and 10 minutes! 2 Cups of Baking Soda 1 Cup of Corn Starch 1 Cups of Cold Water. it is so much cheaper than the store bought model magic! Air dries and can be painted.