Carve a model of a ring in jeweler's wax. Mount the wax model onto a wax rod, called a sprue. With a wax pen, a heated iron similar to a soldering iron, touch the end of the sprue to melt the wax and hold it to the flat side of the ring until joined. Allow to cool.
Mount the sprue onto the flask base. Place the rubber flask base on a working surface and feed the ring-free end of the sprue into the hole at the center. Fit the flask, a cylinder of thin metal, over the rubber base.
Mix investment, a fine, plaster-like material, with room-temperature water to a creamy consistency. Stir slowly to get rid of any air bubbles. Dried investment forms the body of the mold used to cast the ring.
Pick the flask and rubber base up and tilt slightly. Pour the smooth investment on to the bottom side wall of the flask. Rotate the flask while pouring until the flask is full. Place in the flask on the table and tap the sides rhythmically for five minutes to release any air bubbles created during pouring. Allow to dry for 24 hours.
Turn the flask upside down and remove the rubber base, which creates a concave surface. Place the investment inside the kiln, concave-side up. Heat the kiln to 1200 degrees Fahrenheit gradually, in increments of 100 degrees. This dries the investment further and burns out the wax to create the mold cavity. Allow to heat at 1,200 degrees for 1 hour, then lower the heat. Remove the flask with the tongs when the kiln is 400 degrees.
Add of molten metal into the mold while the investment is still warm. Place the flask inside the centrifugal casting machine with the sprue-hole facing the center. Melt the casting metal in a crucible to the proper temperature. Turn the centrifugal machine on. Pour the molten metal slowly into the sprue-hole; the concave surface created by the rubber base around it makes this akin to pouring into a funnel. Follow any specific instructions listed on the centrifugal machine during this process. Turn off once the metal is fully inside the mold.
Allow the mold to cool briefly. Lift out of the machine using tongs and quench the pot of cold water. Shake the mold under water with the tongs to crack and dissolve the fine plaster. Use tongs to remove the cast ring and sprue from the water.
Saw off the sprue with the jewelry saw, file down the nub from the sawed-off sprue with the metal file and scrub away remaining investment from the ring with a hard-bristled toothbrush. Polish the ring to complete.