A trip to Dhamrai - Metal Casting

The crafts are a key part of the village economy. Metalworking, claywork, weaving and basketry are practised nearly everywhere, in villages pots are laid out drying, clay is being mixed or metal is being hammered. Many are skills passed down within family lines, but the numbers of people practicing these skills is reducing due to social and economic factors and materials costs. Much of the work is for export to the cities and further field, some for local consumption. The prices the skilled artisans receive is minimal - labour and craft in Bangladesh is cheap.

Unfortunately we were unable to stay long enough to see the whole of the casting process. which takes nearly 24 hrs. We did see some of the preparation process and evidence of the different stages in the casting process.

Click here to watch a short film: Village Metal Casting.

A wax model is made from beeswax and paraffin (the same materials, but different proportions, used by the jeweller to support the wire work). Sprues and feeders are added to the wax model to assist with the pouring of the molten metal.

The moulds for the artefacts are built up with layers of different clay mixes. Each is allowed to dry between the applications, Initially a fine clay is applied to the wax model, this initial layer has no structural strength but allows for the fine detail of the wax model to be retained. Subsequent layers of clay are mixed with rice husk and Jute fibres to add strength and make it more refractory and resistant to thermal shock. Wire is wrapped around the developing mould and embedded between layers of clay to add strength.

Recycled brass and bronze is broken down and placed into pre fired clay crucibles. The casters select the metals to get an even mix between crucibles should a casting need more than one pour. The clay body for the crucibles again uses rice husk and jute fibres for a more heat resistant mix.

The crucibles are capped with a piece of clay from an old, used crucible then sealed with fresh clay.

When the firing of the furnace starts, a layer of hot coals will be placed at the bottom of the furnace. In large furnaces the caster then covers the coals with a wet, woven reed or a bamboo mat, climbs inside the furnace and has approximately half an hour to pack it with both the sealed crucibles and the moulds before the mat burns through and the heat is too intense for his feet!

The moulds are positioned so that the wax, when heated, will run out of the mould and burn off adding to the feul of the fire and the heat.

When the metal is molten, both the moulds and the crucibles are removed from the furnace, the side of the crucible is pierced to allow the metal to be poured into the mould.

Our next stop for the day was to be Dhamrai Metal Casting Centre, to see more of the casting process.