You can create your own custom molds to make a Jell-O dessert with a three dimensional form. You can use almost any food-safe glass, plastic or metal container to make a successful Jell-O mold with a few simple techniques. Taking some basic precautions and making a Jell-O that sets firm makes releasing the dessert from the mold much easier. How much water the gelatin has been dissolved into and how long it has been chilled to set determines the firmness of the Jell-O mold.
Line the inside of the container with a thin layer of vegetable oil before pressing a single long sheet of aluminum foil to cover the oiled interior. Gently press the aluminum into the container's form to flatten any folds and creases without tearing the foil. Tear off any aluminum foil overhang from the rim in excess of 2 inches of the container.
Place the lined mold and a plate that is large enough to cover the opening into the freezer to get cold while the Jell-O is prepared.
Dissolve the dry Jell-O in boiling water omitting a third of a cup of liquid for every 3 ounce package used. Jell-O's 3-oz. packages call for 1 cup of boiling water in the instructions; reduce this amount to 2/3 cup to produce a firmer Jell-O.
Stir the water and gelatin mixture slowly with a wooden spoon until the granules have dissolved. This process may take as long as two minutes.
Add seven small or five large ice cubes to the mixing bowl for every 3-oz. package of Jell-O being used and continue to stir with the wooden spoon for about a minute or until the majority of the ice has melted. Remove any unmelted ice with the spoon and discard it.
Remove the lined mold from the freezer and slowly pour in the chilled Jell-O mixture in the center of the container. Gently spin the mold from side to side a couple times to release any trapped air.
Move the mold to a refrigerator that maintains temperatures below 38 degrees Fahrenheit and allow it to chill for four hours or until it is firm. Press gently on the surface of the Jell-O with a clean finger to see if it is firm enough to bounce right back.
Retrieve the chilled plate and the set gelatin mold. Wet the plate and exposed surface of the Jell-O using cold water. Cover the open area of the mold with the damp, chilled plate as you invert the mold.
Pull at the aluminum foil around the rim of the mold to release the suction and allow the Jell-O to slide out onto the plate.
Serve the Jell-O dessert right away or return it to the refrigerator to stay cold until time to serve it.
Covering cooling gelatin will cause steam to condensate and accumulate on the surface of the Jell-O. This will result in a bottom layer that is watery and slimy.