I made a clay mask and raku fired it with white crackle glaze, it turned out beautifully. Unfortunately raku fired clay does not reach its ultimate potential strength, so this mask (and others) was very fragile and I was not comfortable wearing or selling it.
After removing the leather lining I placed the mask upon a plaster cast of my own face and covered it with Rebound 25, once the two coats of silicone rubber had cured I used plaster/gauze straps to give the mold a hard outer jacket. Removing the mask from the mold is what finally broke the delicate clay.
I slush cast the rubber mold with jewellry injection wax, which was attached to a base by wax rods called sprues. The entire assembly was placed within a custom flask (a container) and covered by investment (specially formulated high temperature plaster). The filled flask was placed into a kiln and slowly heated to 1350° F, the wax will melt out of the flask and leave a void perfectly replicating the original piece.
Once the flask has been cooled back to 1000° in the kiln the bronze is melted in a crucible inside a gas furnace; just before the metal reaches its boiling point it is removed from the furnace and poured into the hot flask. Once the metal has solidified and cooled to below 800° (indicated by the metal no longer glowing) the flask is quenched in a tub of water. The quenching process shocks the hot investment and blows it off the metal. There is usually still investment left on the bronze, this can be cleaned in an ultrasonic bath or scrubbing with soap and a wire brush.
The sprues can be cut away and the surface of the piece finished in any way desired; I left the front as-cast and sealed it with a spray-on clear coat.