Friday, 21 June 2013

Woodland Art Foundry Part II

Forming the moulds around the wax items.
The wet moulds then went into a charcoal fire. This melted the wax which then just melted out/burnt away and semi fired the mould. The moulds were left in the fire for 3 hours.
 Day 2 began with a copper smelt using a reconstructed Bronze Age pit furnace. Here Dave is digging the pit out in our metalworking hut.

The pit is then filled with charcoal and crushed copper ore (malachite) added.

After lunch, and with the copper made, it was time to cast the objects made yesterday in bronze. The copper made in the AM was added to bronze ingots and used for this casting (bronze being a mixture of copper and tin).

A small clay and dung furnace was used for the casting (the pit used for the smelting could also have been reused for this). The metal was placed in a ceramic crucible and heated in the furnace (again using a forced draft to raise the temperature) until it was red hot and liquidfied!
The bronze was then poured into the moulds. It is vitally important that all the wax has been removed from the moulds before this is done otherwise they will explode, showering molten bronze about. David smells the moulds to check that all the wax has gone (if he smells wax the moulds go back into the fire).

The moulds are placed in 'sand boxes' (a hole filled with sand would also work). This supports the delicate moulds (they are only semi ceramic, not fully fired).

Dave used metal 'shanks' for this but in prehistory wooden and clay covered 'shanks' like these which we have reconstructed could have been used to lift and pour the crucible.

The bronze is quite brittle at this stage so the moulds are tapped rather than smash off using a hammer.

 William (who has been crushing charcoal used for the casting and is did not start out the day this dirty!) with his bronze!
The bronzes then need to be 'fettled'. The details 'chased out' using small chisels and files.
Emma's Celtic design emerging from the metal!

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