The correct option is A mixture of clay, sand, and cow-dung.
Explanation
The lost-wax process (technically known as Cire Perdue) is a traditional metal casting technique used in India since the Bronze Age (Indus Valley Civilization). It allows for the creation of intricate metal sculptures by replacing a wax model with molten metal.Process Analysis:
- Wax Model: First, a detailed model of the object is sculpted using beeswax or a mixture of wax and resin.
- Mould Creation: The wax model is then coated with a specific refractory material to form a mould. In the traditional Indian context, this coating is a mixture of clay, sand, and cow-dung.
- Clay provides the structural shape of the mould.
- Sand ensures the mould can withstand high temperatures (refractoriness).
- Cow-dung acts as a binder and, when burnt, creates porosity in the mould, allowing hot gases to escape during casting.
- Firing (Lost Wax): The coated model is heated. The wax melts and drains out through a designated channel, leaving a hollow cavity inside the clay mould.
- Casting: Molten metal (such as bronze) is poured into this cavity to take the shape of the original wax model.
Key Takeaway:
The outer covering (investment) in the traditional Indian lost-wax process is composed of clay, sand, and cow-dung. This mixture ensures the mould is porous and heat-resistant, preventing it from cracking when molten metal is poured.