You can build a simple burnout kiln for lost-wax jewellery casting. A burnout kiln is used to burn the wax out of the hard mould in which it's encased. Jeweller's wax is first formed into the finished shape of a ring, pendant or earrings. Next a heat resistant, dry plaster is mixed with water and poured over the wax form. When the mould has hardened and dried, it's placed in a kiln and heated enough for the wax to be burnt out of it. This hotplate kiln can get as hot as 704 degrees C, enough heat to burn out jeweller's wax. You'll be surprised how easy this kiln is to make.
Locate a hotplate that has a ceramic stove plate with the heating coil exposed. It's essential that this type of hotplate be used to ensure the kiln will reach a high enough temperature to burn out the wax, according to Don Norris of the moulding and casting online resource, My Heap.
Measure the diameter of the burner, most are usually 6 or 8 inches in diameter.
Take heavy-duty aluminium foil and wrap an unglazed, red clay flower pot. The diameter of the flower pot must match the diameter of the ceramic burner of the hotplate. Wrap the outside only in foil and crimp up to 1 inch of foil around the rim on the inside of the flower pot.
Make a handle for the flower pot for moving it on and off the hotplate. Cut a standard, wire coat hanger just below the twisted wires. Straighten out the coat hanger. Line up the two ends and bend the wire in half. Then bend it in half one more time.
Use a pliers to make two 90-degree angle bends, 3 inches in from each end of the coat hanger. Bend them outwards.
Make another bend 2 inches in from each end. Using a pliers, first bend each of the wire ends down and then back towards the centre.
Bend a 90-degree angle at each end of the wire, 1 inch in from each end. The wire ends are now pointing straight down.
Set the foil wrapped flower pot on its rim. Stick the wire ends of the handle through the foil and into the hole in the bottom of the clay flower pot. Reach into the pot and bend the wires in opposite directions so they're laying flat against the inside, bottom face of the flower pot. On the outside, pull the two long vertical lengths of wire apart so the handle will sit upright on its own.
Set a mould encasing a jeweller's wax form on the burner of the hotplate, set the foil wrapped flower pot over the burner and turn on the hotplate.
Burn out time will depend on the size of the mould and how much wax has been used to create the form of the jewellery piece to be cast.
Use the hotplate kiln in a well-ventilated room or a garage with the door open or run it outdoors. When lifting the foil wrapped flower pot off the hot hotplate use an oven glove or a heat resistant glove to avoid having the handle burn you. The flower pot may crack due to the intense heat. Don't worry the foil will hold it together.