Hi all.
This is my first post on this forum.
This is a very interesting forum for a beginner in metal casting like me.

I need to cast some tens of Aluminum artifacts, and I´ve been investigating the best way to do it without spending a fortune on professionally made molds, because this is just an amateur project.
So, this is something that I have to do all by my self.

The idea is to create a permanent mold, composed of two halves, that I can reuse to cast the Aluminum.

My problem is what material can I use, inside my humble capabilities, to make shuch mold?

Sand it´s out of the list, because I need a much better surface finish that sand can give me.

I have thought about Plaster.
This material can withstand the temperature of the molten Aluminum very well and it gives an excellent surface finish, but it seems that it´s not that good to make reusable molds, because it breaks very easily when demolding.

This way, the obvious material to do the mold halves has to be a metal.
A metal version of the mold can be done, starting with a copy of the part to be produced, doing a Plaster mold in of it in two halves, and then using more plaster to create molds of these two initial Plaster halves.
This way, I will end with a plaster mold of each halve of the first mold, where I can cast liquid metal in order to achieve the two all metallic halves of my final mold.

For this to succeed, I have to find an appropriate metal to do the mold.
It must be a metal capable of being casted on Plaster without destroying it due to very high temperatures, and also a metal on which I can cast the Aluminum into, and demold it without damaging the mold´s inner surfaces due to oxidation or scratching.

Copper and it´s alloys seemed to give nice candidates.
In it´s pure form, Copper has a melting point which I think it is compatible with plaster molds, but it has one problem:
It oxidates very easily at high temperatures, and forms a tarnish layer which will destroy any polished surfaces.

Then there is Brass, and that reminded me that I had some of it on my pocket.
I live in Europe, and our 10, 20 and 50 cents of Euro coins are made of Brass.
I decided to give it a try on a 10 cents coin with my oxi-acetylene torch.
I heat it up until it got red hot and almost melted, then I let it cool, and for my surprise the material still had that characteristic metal shine without any signs of oxidation.

After some search on Wikipedia, I have learned that these coins are made of an alloy composed of 90% Copper, 5% Zinc and 5% Aluminum.
It seems that it´s the Aluminum who gives it that high resistance to oxidation.

I have also found some suppliers who sell bars of similar Brass alloys, and the material doesn´t seem to be very expensive.

So, what do you people think of this? Should I try it?
What problems can I expect by casting Aluminum on a mold made of Brass?
Will it be easy to demold, or are both metals going to weld to each other inside the mold?
Or, are there any other problems that I haven´t even think of?

What about other Copper alloys, like Cupronickel?
This material also seems to be a good candidate.
It has a melting point higher than brass and similar to pure Copper, and it´s corrosion resistance should also be a good one, due to the presence of Nickel and Chromium on it´s alloy.

Now, and before I dive into any experiments, I think it will be a good idea for me to consult with people like you guys, who have the experience and know-how on the field, to see if my ideas make any sense.
So, I will deeply appreciate any advice/opinion that you can offer to me on this subject.

Thanks a lot to all of you.