The process used for casting is known as “Lost wax method”.
• The casting process starts by preparation of the mold.
• A mixture of clay, cow dung and recycled clay from the previously used and broken molds are mixed together.
• This mixture is made to a dough consistency and applied around the achukol of desired shape to make utensils, to make idols and figurine, first step is to sculpt the idols using honey bee wax.
• After the mold is dried, the wax is applied around the mold for desired thickness. In case of idols and figurine, a mixture of clay, finely cut jute sack and recycled clay is applied on the wax.
• For easy and even application of the wax the achukol is mounted in a pit so that it can be rotated.
• Thickness of the wax depends on the product been cast and its kept in sun for drying.
• Once the wax is dried a mixture of clay, finely cut jute sack and recycled clay is applied on the mold.
• Orifices are made on the mold for pouring the molten metal and draining of the molten wax and gases formed during casting.
• On outer surface of the mold, small tile pieces, of broken molds, are fixed to provide necessary strength to withstand against the high temperature while melting the wax in furnace.
• This completed mold is allowed to dry for 4 days under the sun.
• The dried mold is set on fire for melting the wax inside and the molten wax is collected using a vessel, which can be reused, during this 50% of wax is lost. During earlier days the wax used was not collected and it used to evaporate as fumes and gases, so the name Lost wax method.
• The furnace is constructed all around the mold without allowing any gap around it and it is placed slightly elevated from ground in order to set fire below the mold.
• Simultaneously the raw metal or alloys are weighed, according to the desired alloy for casting and filled in crucibles. For bell metal the ratio of copper: tin is 4:1.
• Crucibles are made of special type of mud to withstand very high temperature.
• The ratio of weight of wax and alloy required to cast the product is in the ratio of 1:10 which means if the wax model weighs 1 kg then the casting will weigh around 10kg.
• Crucibles are filled with the required quantity of the metal and placed in the furnace for melting.
• Looking at the color of the flame in the fire vent craftsmen can easily identify whether the raw metal is molten are not.
• The normal flame is reddish yellow but the flame coming out from the molten metal is distinctively greenish blue in color.
• After the molten wax is completely drained, the mold is moved to a new pit which is made to accommodate the mold for casting.
• The drain holes are plugged and mold is placed in the pit covering with sand all around firmly. Only the holes for pouring the molten metal and vent holes are spared and rest are covered completely with the sand.
• The crucible is removed from the furnace and molten metal is poured into the mold through the holes provided.
• At the time of pouring, wet jute sack is used as a shield from flames and spilling of molten metal on to the feet of the craftsman.
• Molten metal is poured into the mold while the mold is still hot in order to avoid sudden cooling and breakage of the casting.
• The casting is allowed to cool & set for 12 hours and mold is removed from the pit and casting is taken out of the mold.
• The casting obtained is unfinished and further processing is required.
• The clay sticking to it is scraped and the extra projections are cut off using a hand grinding machine.
• Any rough edges present are removed and polishing is done with liquid metal polish.
