Workshop Technology
Aluminium is the best material for making patterns because it is

Corrosion resistant
Light in weight
Easy to work
All of the listed here

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Workshop Technology
The purpose of a riser is to

Feed the molten metal to the casting in order to compensate for the shrinkage
Deliver molten metal into the mould cavity
Act as a reservoir for the molten metal
Deliver the molten metal from pouring basin to gate

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