Purchase fusible glass on-line or through art supply stores. Prices will vary depending on the size and color. You will also need a glass grinder, which can be purchased online for around $110 USD.
Measure the length of the stainless steal glass mold from the bottom edge to the rim. Multiply that length by 2 and then subtract 4 inches from the total. The size of the vase should not be larger then the stainless steel glass mold.
Cut a square piece of glass from your fusible glass that is equal in length on both sides to the total from your calculation. Finish the cut by breaking the glass apart with breaking pliers.
Smooth the edges of the glass with a glass grinder.
Wash the glass with a non-abrasive soap and water. Allow to dry.
Place the stainless steel glass mold in the center of the kiln so that the bottom if facing up.
Lay piece of cut fusible glass on top of the mold. Center it just right so that it balances on the mold.
Close the lid and turn on the kiln. Slowly increase the temperature to 500 degrees Fahrenheit. You must bring the temperature up slowly to avoid breaking in the glass. Raise the temperature by 50 degrees every few minutes. Once the kiln reaches 500 degrees let it sit or "soak" for 20 minutes.
Increase the temperature to 700 degrees Fahrenheit, 50 degrees at a time. Allow the vase to soak for another 20 minutes once it reaches 700 degrees. Soak for another 20 minutes at 1020 degrees Fahrenheit.
Turn the kiln up to 1350 degrees after the last soak.
Put on your kiln safety goggles and open the kiln lid at around 1200 degrees to peek at the glass. It is important to view the glass around this temperature as the glass will start to move around. Peek at the vase every 10 minutes, until it has draped down over the side of the mold enough that you like the look of it.
Open the lid to allow the kiln temperature to drop to 1100 degrees Fahrenheit. Lower the kiln temperature to 500 degrees and close the lid again. At 500 degrees, open the kiln to check on the vase. Turn off the kiln, close the lid and allow the it to cool down on.
Remove the piece once it is completely cooled. Pull the piece off of the glass mold. Run it under water while twisting it off, if the vase is resisting.