[metalriffzz]

I'm looking to buy a casting crucible to melt aluminum and possibly copper, and I have two choices:

The cheaper alumnia crucible with a max working temp of 1750 C
or
The more expensive MgO crucible with a max temp of 2500C

I know I could probably get away with the cheaper one at least for aluminum but I'm looking for some second opinions.

[constant thinker]

http://www.backyardmetalcasting.com/index.html

Check that site out. May help some.

[Grumples]

The MP of aluminum is about 700C, while the MP of copper is about 1100C, both well within the alumina crucible's heat range.  

You may also want to look into various graphite crucibles- I know for a fact that some of those can take up to 3000C (graphite crucibles are typically very cheap if they are small, but get exponentially more expensive as the get bigger).

[metalriffzz]

Yeah those graphite ones don't look too bad. What about durability? I think I might spring for an electromelt furnace if the opporitunity presents itself.

[limpet chicken]

For melting the metals, look in the technochem section of www.sciencemadness.org for posts by Axehandle, he has built a few furnaces himself, pretty good ones too