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BioPatent Communications

Ancient South Asian

Lost Wax Casting Techniques
by Gary Baker, Esq. - Patent Attorney

During my trip to South India, I had the great pleasure of visiting a family that has made traditional Hindu religious statues on their property for at least 5 generations.  The shape and proportions of the statues are based on ancient Sanskrit formulas.  Briefly, this lost wax process comprises: preparation of original wax figures, encasing the figures in fine river silt mud, drying the mud, melting out the wax to form a hollow mold, melting a combination of metals with a charcoal fire, pouring the molten metal to fill the mold, hand tooling details on the crude casting, and laboriously hand finishing details into the solid metal statues.

I.  WAX FIGURE - The artist, using the Sanskrit formulas particular to the subject god or goddess, first creates a stick figure in the intended pose out of bees wax.  The body parts are filled out, again according to ancient proscribed dimensions, by application of additional warmed wax layers to the stick figure.  Surface details are blocked out without a high degree of detail. 

II. INVESTING THE FIGURE - The wax original of the statue is sealed in a cocoon of mud (from the near-by river) by careful hand packing.  Two wax sprue sticks are left extending between the wax figure and the exterior of the mud casing to provide channels to receive the molten metal during the later pouring step.  The mud covering is supported with a few wrappings of metal wire to reduce cracking during the drying step and to strengthen the mold.  The encased wax figure is set out to dry in the sun for 20 days.

III. MELT OUT - A furnace is made from a hand-powered rotary fan blowing through a vent tube into a brick-lined chamber of burning charcoal.  The furnace is used to melt wax out of the mold, bake and harden the mold, and to melt the metals for pouring into the mold.   The sun-dried mold is placed in the furnace hole with the sprues facing down.  As the furnace heats the mold, the internal wax figure is melted and pours out holes remaining when the sprues are melted away.  The mold is heated for several hours until all wax residue is vaporized or burned away. 

IV. MOLTEN METAL - The combination of metals is weighed out and place together in a crucible for melting in the charcoal furnace.  Traditionally, statues were supposed to be poured from a "5-metal" combination of equal weight parts gold, silver, tin, copper and zinc.   Because gold is expensive, only a token sprinkle is added to an essentially 4-metal combination, a little rich in copper and light on silver.  However, if too little silver is added, the metal will loose it's tell-tale dark patina and will clunk when struck, instead of producing a sweet chime. 

V. POURING - The pre-heated mold is placed in a hole in the ground and surrounded with loose dirt with the sprue holes facing up.  Cherry-red molten metals are poured into one sprue hole until it flows up out of the other hole.  The cast statue is left alone in the dirt for a couple hours to slowly cool.  The crude statue is released by striking the mold with a hammer. 

VI. FINISHING - Now the laborious part.  The big surprise for me was to see that much of the fine detail is not present in the wax figures.  Mud casting media (investment) is not fine grain and does not provide high resolution details.  The feet of figures were merely box-feet; the faces were blank.  Finishing is done with increasingly fine work - 1) cutting off sprues; 2) chiseling and engraving the face, toes, fingers, clothing patterns, crowns, etc.; 3) assembly of separately cast components; 4) if there is a defect of mistake in the casting, new material is brazed over the defect and the correct contours are carved into the overlay; 5) course grinding and filing; 6) course sanding to fine sanding, by hand; and, 7) course polishing to fine polishing.  This requires an incredible amount of labor and artistry. 

The artists can be proud of their work.  Each piece is a unique one-of-a-kind work of art. 

Shown above are the master artist and his two sons with a statue of Ardhanarishwara.  Parvati, the wife of Shiva, felt bad when she thought Shiva had won a dance contest between them.  So Shiva took on a half man, half woman form to show the division in nature between male and female is but an illusion. 

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