Form the molding clay in the palm of your hand to resemble a thick hamburger patty. It should measure about 2 to 3 inches thick by 4 inches wide.
Press the item you have selected, face down, into the top surface of your molding clay patty. Select a 3D item such as figurines, jewelry pieces and even your pet's paw. Remove the item to reveal the intricately indented mold. Let it dry for 30 minutes.
Add the plaster of Paris mix, which is dried and packaged in craft stores, into the 2 qt. mixing bowl. Add the water and mix the solution briskly for one minute.
Spray the surface of your mold with nonstick cooking spray to make it easier to release the plaster item.
Pour the plaster batter into the mold, filling it as full as you can get. It's okay if you spill a little bit, because the important part of your plaster shape is inside the mold. Place it somewhere dry and safe for up to two days before trying to release it from the mold.