Making a perfect, smooth cube

[ikkiyikki]

Hi guys, this is my first post and I'm hoping this is the right place to ask.

I am putting together a collection of elements that I want to display in little acrylic blocks like this one:
http://upload.wikimedia.org/wikipedia/c ... c_cube.jpg

These cubes are perfectly smooth and clear but are very expensive to buy ready-made with the samples embedded. It would be a lot cheaper (and fun!) if I could make my own.

What steps would I need to make a mold that would give seamless cubes? Or are the seams unavoidable and later buffed out?

Any help would be great... would love to show my progress from what I learn here!

Ras
ps. the cubes are 2 inches on a side

[Fleafa]

The seam will have been buffed out.